Method and apparatus for coding image information, method and apparatus for decoding image information, method and apparatus for coding and decoding image information, and system of coding and transmitting image information

ABSTRACT

An image decoding apparatus for decoding a bit stream includes a receiving unit that receives the bit stream and a weight parameter that is added to a luma quantization parameter. The image decoding apparatus also includes a decoding unit that decodes the bit stream and generates a chroma component of quantized coefficients. Further, the image decoding apparatus includes a dequantization unit that performs dequantization on the chroma component of quantized coefficients using a chroma quantization parameter calculated on the basis of a luma quantization parameter weighted by the weight parameter. In addition, the image decoding apparatus includes a transform unit that performs an inverse orthogonal transform.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 13/370,174,filed Feb. 9, 2012, which is a continuation of application Ser. No.12/620,431, filed Nov. 17, 2009, now U.S. Pat. No. 8,139,636, which is acontinuation of application Ser. No. 11/836,467, filed Aug. 9, 2007, nowU.S. Pat. No. 7,733,955, which is a continuation of application Ser. No.10/304,950, filed Nov. 27, 2002, now U.S. Pat. No. 7,295,609, the entirecontents of each of which is incorporated herein by reference. Thisapplication also claims priority to Japanese Patent Application Nos.2001-367868, filed Nov. 30, 2001, and 2002-124641, filed Apr. 25, 2002.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for coding imageinformation, a method and apparatus for decoding image information, amethod and apparatus for coding and decoding image information, and asystem for coding and transmitting image information, for use inreceiving, via a network medium such as satellite broadcasting, cabletelevision, or the Internet, image information (bit stream) compressedby means of an orthogonal transform such as a discrete cosine transformor a Karhunen-Loeve transform and motion compensation according to theMPEG (Moving Picture Experts Group) standard or the standard H.26x, orfor use in processing image information on a storage medium such as anoptical disk, a magnetic disk, or a flash memory.

2. Description of the Related Art

In recent years, techniques of transmitting or storing digital imageinformation in a highly compressed form have been popular in variousapparatuses used in information distribution such as broadcasting andalso in home use apparatuses. In a typical technique based on the MPEGstandard, image information is compressed using redundancy of the imageinformation by means of an orthogonal transform such as a discretecosine transform and motion compensation.

MPEG2 (ISO/IEC13818-2) is a standard for general-purpose imageinformation coding. The MPEG2 standard is designed to deal with imageinformation in various forms and fashions such as an interlaced image, asequentially scanned image, a standard-resolution image, and ahigh-resolution image, and the MPEG2 is employed in a wide range ofapplications including professional applications and consumerapplications. The MPEG2 compression scheme allows an interlacedstandard-resolution image with 720×480 pixels to be converted into acompressed image at a bit rate of 4 to 8 Mbps and an interlacedhigh-resolution image with 1920×1088 pixels to be converted into acompressed image at a bit rate of 18 to 22 Mbps, with a high compressionratio while maintaining high image quality.

The MPEG2 standard has been designed to code image information with highquality for use mainly in broadcasting, and the MPEG2 standard does notsupport coding at lower bit rates (higher compression rates) than aresupported by the MPEG1 standard. That is, coding with very highcompression ratios is not supported by the MPEG2 standard. However, withincreasing popularity of portable terminals, there is an increasing needfor coding with high compression ratios at low bit rates. To meet such aneed, MPEG4 standard has been established. The image information codingscheme based on MPEG4 was employed as an international standard (ISO/IEC14 496-2) in December 1998.

In recent years, work for establishing the H.26L standard (ITU-T Q6/16VCEG) for coding of image information for use in video conferences hasbeen done. It is known that the H.26L standard provides high codingefficiency compared with the conventional coding schemes such as MPEG2or MPEG4 coding, although H.26L needs a greater amount of computation incoding and decoding. As one of activities associated with MPEG4, effortsare now being made to establish a higher-compression coding standard(Joint Model of Enhanced-Compression Video Coding) based on H.26L, whichwill support some functions which are not supported by the H.26Lstandard.

Referring to FIG. 19, a conventional image information coding apparatususing an orthogonal transform such as a discrete cosine transform or aKarhunen-Loeve transform and motion compensation is described below.

As shown in FIG. 19, the conventional image information coding apparatus201 includes an analog-to-digital converter 211, a frame rearrangementbuffer 212, an adder 213, an orthogonal transformer 214, a quantizer215, a lossless coder 216, a storage buffer 217, a dequantizer 218, aninverse orthogonal transformer 219, a frame memory 220, a motionprediction compensator 221, and a rate controller 222.

In FIG. 19, the analog-to-digital converter 211 converts an input imagesignal into a digital signal. The frame rearrangement buffer 212rearranges frames depending on the GOP (Group of Pictures) structure ofthe compressed image information output from the image informationcoding apparatus 201. When the frame rearrangement buffer 212 receives aframe to be intra-coded, the frame rearrangement buffer 212 supplies theimage information of the entire frame to the orthogonal transformer 214.The orthogonal transformer 214 performs an orthogonal transform such asa discrete cosine transform or a Karhunen-Loeve transform on the imageinformation and supplies resultant transform coefficients to thequantizer 215. The quantizer 215 quantizes the transform coefficientsreceived from the orthogonal transformer 214.

The lossless coder 216 performs lossless coding by means of variablelength coding or arithmetic coding on the quantized transformcoefficients and supplies the resultant coded transform coefficients tothe storage buffer 217. The storage buffer 217 stores the received codedtransform coefficients. The coded transform coefficients are output ascompressed image information from the storage buffer 18.

The behavior of the quantizer 215 is controlled by the rate controller222. The quantizer 215 also supplies the quantized transformcoefficients to the dequantizer 218. The dequantizer 218 dequantizes thereceived transform coefficients. The inverse orthogonal transformer 219performs an inverse orthogonal transform on the dequantized transformcoefficients thereby producing decoded image information and stores theresultant decoded image information into the frame memory 220.

On the other hand, image information of those frames to beinterframe-coded is supplied from the frame rearrangement buffer 212 tothe motion prediction compensator 221. At the same time, the motionprediction compensator 221 reads image information to be referred tofrom the frame memory 220 and performs motion prediction compensation toproduce reference image information. The motion prediction compensator221 supplies the reference image information to the adder 213. The adder213 produces a difference signal indicating the difference between theimage information and the reference image information. At the same time,the motion prediction compensator 221 also supplies the motion vectorinformation to the lossless coder 216.

The lossless coder 216 performs lossless coding by means of variablelength coding or arithmetic coding on the motion vector informationthereby producing information to be put in a header of the compressedimage information. The other processes are performed in a similar mannerto compressed image information to be intra-coded, and thus they are notdescribed herein in further detail.

Referring to FIG. 20, an image information decoding apparatuscorresponding to the above image information coding apparatus 201 isdescribed below.

As shown in FIG. 20, the image information decoding apparatus 241includes a storage buffer 251, a lossless decoder 252, a dequantizer253, an inverse orthogonal transformer 254, an adder 255, a framerearrangement buffer 256, a digital-to-analog converter 257, a motionprediction compensator 258, and a frame memory 259.

In FIG. 20, compressed image information input to the storage buffer 251is transferred to the lossless decoder 252 after being temporarilystored in the storage buffer 251. The lossless decoder 252 decodes thereceived compressed image information by means of variable lengthdecoding or arithmetic decoding in accordance with the format of thecompressed image information and supplies the resultant quantizedtransform coefficients to the dequantizer 253. In a case in which theframe supplied to the lossless decoder 252 is an interframe-coded frame,the lossless decoder 252 also decodes the motion vector informationdescribed in the header of the compressed image information and suppliesthe resultant decoded information to the motion prediction compensator258.

The dequantizer 253 dequantizes the quantized transform coefficientssupplied from the lossless decoder 252 and supplies the resultanttransform coefficients to the inverse orthogonal transformer 254. Theinverse orthogonal transformer 254 performs an inverse orthogonaltransform such as an inverse discrete cosine transform or an inverseKarhunen-Loeve transform on the transform coefficients in accordancewith the predetermined format of the compressed image information.

In a case in which a given frame is an intra-coded frame, the imageinformation subjected to the inverse orthogonal transform is stored inthe frame rearrangement buffer 256. The image information stored in theframe rearrangement buffer 256 is supplied to the digital-to-analogconverter 257, which converts the received image information into analogform and outputs the resultant analog image information.

On the other hand, in a case in which the frame being processed is aninterframe-coded frame, the motion prediction compensator 258 producesan reference image on the basis of the motion vector informationsubjected to the lossless decoding process and the image informationstored in the frame memory 259. The resultant reference image issupplied to the adder 255. The adder 255 adds the received referenceimage to the output of the inverse orthogonal transformer 254. The otherprocesses are performed in a similar manner to intraframe-coded frames,and thus they are not described in further detail herein.

The MPEG2 standard does not include detailed definition of quantization,and only dequantization is defined in detail. Therefore, in practicalquantization processing, quantization characteristics are varied byvarying some parameters associated with quantization so as to achievehigh image quality or accomplish coding so as to reflect visualcharacteristics. The dequantization process according to the MPEG2standard is described below.

In quantization of DC coefficients of intra macroblocks according to theMPEG2 video standard, the quantization accuracy can be specified on apicture-by-picture basis. In quantization of the other coefficients, thequantization accuracy of each coefficient can be controlled bymultiplying each element of a quantization matrix, which can bespecified on a picture-by-picture basis, by a quantization scale whichcan be specified on a macroblock-by-macroblock basis.

DC coefficients of each intra macroblock are dequantized in accordancewith equation (1) described below.F″[0][0]=intra_dc_mult×QF[0][0]  (1)

In equation (1), F″[0] [0] denotes a representative quantization valueof a DC coefficient, and QF[0] [0] denotes a level number of therepresentative quantization value of the DC coefficient. intra_dc_multdenotes a value which is defined, as shown in FIG. 21, depending on aparameter intra_dc_precision which can be set to specify thequantization accuracy of DC coefficients on the picture-by-picturebasis.

In the MPEG1 standard, intra_dc_precision is allowed only to be 0, andthe corresponding accuracy (B bits) is not high enough to code an imagewhose luminance level varies gradually while maintaining high imagequality. In the MPEG2, to avoid the above problem, quantization accuracyfor DC coefficients as high as 8 to 11 bits can be specified viaintra_dc_precision, as shown in FIG. 21. However, the highestquantization accuracy is allowed only in the 4:2:2: format, and thequantization accuracy is limited to the range from 8 to 10 bits exceptfor the high profile for use in applications which need high imagequality.

The other coefficients of each intra macroblock are dequantized inaccordance with equation (2) described below.F″[u][v]=((2×QF[u][v]+k)×W[w][u][v])×quantiser_scale)/32  (2)

In equation (2), F″[u] [v] denotes a representative quantization valueof a (u, v)-coefficient and QF[u] [v] denotes a level number of therepresentative quantization value of the (u, v)-coefficient. The valueof k is given by the following equation (3).

$\begin{matrix}{k = \left\{ \begin{matrix}{0\text{:}} & {{for}\mspace{14mu}{intra}\mspace{14mu}{macroblocks}} \\{{{Sign}\left( {{{QF}\lbrack u\rbrack}\lbrack v\rbrack} \right)}\text{:}} & {{for}\mspace{14mu}{non}\text{-}{intra}\mspace{14mu}{macroblock}}\end{matrix} \right.} & (3)\end{matrix}$

In equation (2) described above, W[w][u][v] denotes a quantizationmatrix and quantiser_scale denotes a quantization scale. Thequantization characteristic are controlled by those parameters.

The parameter k has a value of 1, 0, or −1 in non-intra macroblocks,depending on the sign of QF[u][v]. For example, when. QF[u][v] has avalue of −2, −1, 0, 1, or 2, F″[u][v] has a value of −5m, −3m, 0, 3m, or5m (where m is a constant). Thus, there is a dead zone near 0.

The quantization matrix defines relative quantization accuracy fordiscrete cosine coefficients within a block. Use of the quantizationmatrix allows discrete cosine coefficients to be quantized with agreater quantization step in a high-frequency range, in which a largequantization step does not result in significant visually perceptibledegradation, than in a low-frequency range in which a large quantizationstep results in visually perceptible degradation. That is, it becomespossible to vary the quantization characteristic so as to match thevisual characteristics. The quantization matrix can be set on apicture-by-picture basis.

In the case of the 4:2:0 format according to MPEG1 or MPEG2, two typesof quantization matrices can be set: one is for intra macroblocks andthe other for non-intra macroblocks. In the 4:2:2 format and the 4:4:4format, two types of quantization matrices can be defined independentlyfor each of the luminance signal and the color difference signal, andthus a total of four quantization matrices can be defined. w(0, 1, 2, 3)in W[w] [u] [v] denotes one of 4 matrices.

In the MPEG2 standard, the default values of the quantization matrix forintra macroblocks are defined as shown in FIG. 22, and those fornon-intra macroblocks as shown in FIG. 23. As described earlier, thequantization matrices can be set on the picture-by-picture basis.However, when no quantization matrix is set, the default valuesdescribed above are employed. When the default values are employed, ascan be seen from FIGS. 22 and 23, weighting is performed only for intramacroblocks.

In the MPEG2 Test Model 5 (ISO/IEC JTC/SC29/WG11/N0400), thequantization matrix for non-intra macroblocks are defined as shown inFIG. 24. Unlike the quantization matrix shown in FIG. 22, thequantization matrix shown in FIG. 24 has weighted values.

A parameter quantiser_scale is a parameter to control the amount of datagenerated by quantization, by scaling the quantization characteristic,wherein the quantization scale is given by a parameter quantiser_scalewhich is determined by a parameter q_scale_type set on thepicture-by-picture basis and a parameter quantiser_scale_code set on themacroblock-by-macroblock basis. FIG. 25 shows the relationships amongthose parameters.

As shown in FIG. 25, when q_scale_type=0, quantization is performed in alinear fashion. In this case, as with MPEG1, quantiser_scale (2 to 62)is set to be equal to 2 times quantiser_scale_code (1 to 31).

On the other hand, when q_scale_type=1, quantization is performed in anonlinear fashion. In this mode, quantiser_scale is varied in smallsteps when quantiser_scale_code has a small value while quantiser_scaleis varied in large steps when quantiser_scale_code has a large value,and thus quantiser_scale_code (1 to 31) is converted intoquantiser_scale having a greater range (1 to 112) than in the linearquantization. This mode was newly introduced when the MPEG2 standard wasestablished to make it possible to perform fine control of thequantization scale in a small quantization scale range at high rates,and to employ a large quantization scale when a very complicated imageis coded. That is, the mode of q_scale_type=1 allows the bit rate to becontrolled in a more optimal fashion than can be by MPEG1.

In H.26L, in contrast to MPEG2, coding is performed on the basis of 4×4discrete cosine transform. More specifically, when quantized pixelvalues or quantized difference pixel values are given as (a, b, c, d),and transform coefficients are given as (A, B, C, D), a discrete cosinetransform is performed in accordance with the following formula.

$\begin{matrix}\left\{ \begin{matrix}{A = {{13a} + {13b} + {13c} + {13d}}} \\{B = {{17a} + {7b} - {7c} + {17d}}} \\{C = {{13a} - {13b} - {13c} + {13d}}} \\{D = {{7a} - {17b} + {17c} - {7d}}}\end{matrix} \right. & (4)\end{matrix}$

If coefficients obtained via the transform are represented by (a′, b′,c′, d′), processing corresponding to an inverse discrete cosinetransform is performed according to equation (5).

$\begin{matrix}\left\{ \begin{matrix}{a^{\prime} = {{13A} + {17B} + {13C} + {7D}}} \\{b^{\prime} = {{13A} + {7B} - {13C} - {17D}}} \\{c^{\prime} = {{13A} - {7B} - {13C} + {17D}}} \\{d^{\prime} = {{13A} - {17B} + {13C} - {7D}}}\end{matrix} \right. & (5)\end{matrix}$

Thus, between a′ and a, there is a relationship represented by equation(6).a′=676a  (6)

The relationship between a′ and a represented by equation (6) arisesfrom the fact that equations (4) and (5) are not normalized.Normalization is performed when a shift operation is performed afterdequantization, as will be described in detail later.

In H.26L, a parameter QP used in quantization and dequantization isdefined such that QP takes a value in the range of 0 to 31 and thequantization step size is increased by 12% each time QP increases by 1.In other words, the quantization step size increases by a factor of 2each time QP increases by 6.

The values of QP embedded in compressed image information are for theluminance signal, and thus they are denoted by QP_(luma). On the otherhand, in contrast to QP_(luma), QP for the color difference signal, thatis, QP_(chroma) takes following values.

QP_(luma): 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17,18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31

QP_(chroma): 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 17, 18, 19, 20, 20, 21, 22, 22, 23, 23, 24, 24, 25, 26

Hereinafter, QP_(luma) will be referred to simply as QP unlessdistinction is necessary.

In H.26L, two arrays A(QP) and B(QP) for use inquantization/dequantization are defined as described below.

A(QP=0, . . . , 31): 620, 553, 492, 439, 391, 348, 310, 276, 246, 219,195, 174, 155, 138, 123, 110, 98, 87, 78, 69, 62, 55, 49, 44, 39, 35,31, 27, 24, 22, 19, 17

B(QP=0, . . . , 31): 3881, 4351, 4890, 5481, 6154, 6914, 7761, 8718,10987, 12339, 13828, 15523, 17435, 19561, 21873, 24552, 27656, 30847,34870, 38807, 43747, 49103, 54683, 61694, 68745, 77615, 89113, 100253,109366, 126635, 141533

Between the arrays A(QP) and B(QP), there is a relationship representedby equation (7).A(QP)×B(QP)×676²=2⁴⁰  (7)

Using the array A(QP) in equation (7), the coefficient K is quantizedaccording to equation (8).LEVEL=(K×A(QP)+f×2²⁰)/2²⁰  (8)

In equation (8), |f| has a value in the range of 0 to 0.5, wherein thesign of f is equal to the that of K.

Dequantization is performed as shown in equation (9).K′=LEVEL×B(QP)  (9)

After calculating equation (9), 20-bit shifting and rounding areperformed on the coefficient K′. The sequential process including theorthogonal transform and the quantization is designed such that nooverflow occurs when the process is performed in 32 bits.

Note that the standard for the quantization/dequantization isprovisional, and the overflow-free data length will probably be 16 bitsin the final version of the standard.

In quantization/dequantization according to the H.26L standard, unlikethe MPEG2 standard, weighting of orthogonal transform coefficients usinga quantization matrix is not allowed, and thus it is impossible toefficiently perform quantization on the basis of visual characteristics.

The above-described quantization according to the H.26L corresponds toMPEG2-based quantization: 2.5019, 2.8050, 3.1527, 3.5334, 3.9671,4.4573, 5.0037, 5.6201, and 6.3055. However, in the MPEG2, the dynamicrange of the nonlinear quantization is 1 to 112, and thus the range ofquantization according to MPEG2 cannot be entirely covered byquantization according to H.26L.

This causes a spurious contour line to be created in an image includinga part whose pixel value varies gradually. Another problem is thathigh-efficient compression is impossible at low bit rates.

In view of the above, it is an object of the present invention toprovide a technique of preventing a spurious contour line from beingcreated in an image including a part with gradually varying pixel valuesand a technique of performing high-efficient compression at low bitrates.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided afirst image information coding apparatus/method for coding imageinformation by dividing an input image signal into blocks, performing anorthogonal transform on the blocks on a block-by-block basis, andquantizing orthogonal transform coefficients, wherein, in thequantization, weighting is performed for each component of theorthogonal transform coefficients by means of an addition operation on aparameter QP specifying one of elements of a series of numbers arrangedin accordance with a predetermined rule in correspondence withquantization step sizes.

In this first image information coding apparatus/method, preferably, anarray A(QP) consisting of elements having values which increase ordecrease by a % with increasing of the value of the parameter QP by 1 isused as the sequence of numbers corresponding to the quantization stepsizes, and in the quantization, the orthogonal transform coefficients Kare multiplied by the values of the array A(QP) and the resultantproduct is quantized.

In this first image information coding apparatus/method, when theparameter QP exceeds an upper limit or a lower limit, the array A(QP)may be extended so as to have an extended value or values determined onthe basis of the increasing or decreasing ratio of the original arrayA(QP), and the extended value or values of the A(QP) may be used for theexceeding value or values of the parameter QP.

That is, in this first image information coding apparatus/method, thequantization is performed such that the orthogonal transform coefficientis first multiplied by the value of the array A(QP) and then theresultant product is quantized, wherein QP is a parameter specifying oneof elements of a series of numbers arranged in accordance with apredetermined rule in correspondence with quantization step sizes andthe value of the array A(QP) increases or decreases by α% withincreasing of the value of the parameter QP by 1.

When the parameter QP exceeds an upper limit or a lower limit, the arrayA(QP) may be extended so as to have an extended value or valuesdetermined on the basis of the increasing or decreasing ratio of theoriginal array A(QP), and the extended value or values of the A(QP) maybe used for the exceeding value or values of the parameter QP.

The parameter QP may include a parameter QP_(luma) applied to aluminance signal and a parameter QP_(chroma) applied to a colordifference signal, and the quantization may be performed such that aparameter QQP_(luma)(i, j) is calculated by adding a weighting arrayW(i, j) to the array of the parameter QP_(luma) corresponding to therespective components of the luminance signal of each block, a parameteron QQP_(chroma) (i, j) is calculated by adding the weighting array W(i,j) to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal of each block, andquantization weighting is performed using the resultant parameterQQP_(luma)(i, j) and the resultant parameter QQP_(chroma)(i, j).

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds a predetermined value QQP_(chroma) _(—) _(max), the weightedquantization may be performed using the predetermined value QQP_(chroma)_(—) _(max) as the parameter QQP_(chroma) (i, j).

In the first image information coding method/apparatus, the quantizationmay be performed such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship are preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

dequantization corresponding to the quantization is to be performed inaccordance with the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient, andwherein when the parameter QQP_(chroma)(i, j) obtained via thecalculation exceeds the predetermined value QQP_(chroma) _(—) _(max), acommon ration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma) (i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{{chroma}\;\_\;\max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{{chroma}\;\_\;\max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{{chroma}\;\_\;\max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma _ max )) = round(A(QQP_(chroma _ max )) × r^(QQP_(chroma)(i, j) − QQP_(chroma _ max )))where round( ) denotes a round-into-integer function, and

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))+f×2^(m))/2^(m).

According to another aspect of the present invention, there is provideda second image information coding method/apparatus for coding imageinformation by dividing an input image signal into first blocks,performing a first orthogonal transform on the first blocks on ablock-by-block basis, forming second blocks including only DC componentsof orthogonal transform coefficients obtained via the first orthogonaltransform, and performing a second orthogonal transform on the secondblocks; and quantizing the coefficients of AC components obtained viathe first orthogonal transform and quantizing the coefficients of the DCcomponent obtained via the second orthogonal transform, wherein, in thequantization, coefficients of the AC components obtained via the firstorthogonal transform are weighted differently from the coefficients ofthe DC components obtained via the second orthogonal transform.

In this second image information coding method/apparatus, coefficientsof DC components obtained via the first orthogonal transform areextracted, and the second orthogonal transform is performed on theextracted coefficients, and the coefficients of AC components obtainedvia the first orthogonal transform and the coefficients of DC componentsobtained via the second orthogonal transform are quantized in weightedfashion such that the coefficients of AC components are weighteddifferently from the coefficients of DC components.

In the second image information coding method/apparatus, thequantization of the coefficients of the AC components may be performedusing, as the parameter QP, a parameter QP_(luma) for a luminance signaland a parameter QP_(chroma) for a color difference signal, and thequantization of the coefficients of the DC components may be performedusing, as the parameter QQP, a parameter QQP_(luma)(i, j) for theluminance signal and a parameter QQP_(chroma)(i, j) for the colordifference signal, wherein the parameter QQP_(luma)(i, j) is obtained byadding a weighting array W(i, j) as the parameter X to the array of theparameter QP_(luma) corresponding to the respective components of theluminance signal of each block, and the parameter QQP_(chroma)(i, j) isobtained by adding the array W(i, j) as the parameter X to the array ofthe parameter QP_(chroma) corresponding to the respective components ofthe color difference signal of each block.

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max), thequantization of the coefficients of DC components may be performed usingthe predetermined value QQP_(chroma) _(—) _(max) as the parameterQQP_(chroma)(i, j).

In the second image information coding method/apparatus, thequantization may be performed such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship are preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization of the coefficients of AC components is performed inaccordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output, dequantization of the coefficients of ACcomponents, corresponding to the quantization, is to be performed inaccordance with the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient, andwherein when the parameter QQP_(chroma)(i, j) obtained via thecalculation exceeds the predetermined value QQP_(chroma) _(—) _(max), acommon ration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{{chroma}\;\_\;\max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{{chroma}\;\_\;\max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{{chroma}\;\_\;\max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma _ max )) = round(A(QQP_(chroma _ max )) × r^(QQP_(chroma)(i, j) − QQP_(chroma _ max )))where round( ) denotes a round-into-integer function, and

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))+f×2^(m))/2^(m).

According to another aspect of the present invention, there is provideda first image information decoding method/apparatus for decodingcompressed image information which has been coded via a processincluding the steps of dividing an input image signal into blocks,performing an orthogonal transform on the blocks on a block-by-blockbasis, and quantizing resultant orthogonal transform coefficients, thedecoding process including the steps of performing dequantization andperforming an inverse orthogonal transform, wherein, in thedequantization, weighted dequantization is performed on each componentof the quantized coefficients by means of an addition operation on aparameter QP specifying one of elements of a series of numbers arrangedin accordance with a predetermined rule in correspondence withquantization step sizes.

In this first image information decoding method/apparatus, an arrayB(QP) consisting of elements having values which increase or decrease byβ% with increasing of the value of the parameter QP by 1 may be used asthe sequence of numbers corresponding to the quantization step sizes,and the dequantization may be performed by multiplying the quantizedcoefficients by the values of the array B(QP).

In this first image information decoding method/apparatus, when theparameter QP exceeds an upper limit or a lower limit, the array B(QP)may be extended so as to have an extended value or values determined onthe basis of the increasing or decreasing ratio of the original arrayB(QP), and the extended value or values of the B(QP) may be used for theexceeding value or values of the parameter QP.

That is, in this first image information decoding method/apparatus, thedequantization is performed such that the quantized coefficient ismultiplied by the value of the array B(QP), wherein QP is a parameterspecifying one of elements of a series of numbers arranged in accordancewith a predetermined rule in correspondence with quantization stepsizes, and the value of the array B(QP) increases or decreases by β%with increasing of the value of the parameter QP by 1.

When the parameter QP exceeds an upper limit or a lower limit, the arrayB(QP) may be extended so as to have an extended value or valuesdetermined on the basis of the increasing or decreasing ratio of theoriginal array B(QP), and the extended value or values of the B(QP) maybe used for the exceeding value or values of the parameter QP.

The parameter QP may include a parameter QP_(luma) applied to aluminance signal and a parameter QP_(chroma) applied to a colordifference signal, and the dequantization may be performed such that aparameter QQP_(luma)(i, j) is calculated by adding a weighting arrayW(i, j) to the array of the parameter QP_(luma) corresponding to therespective components of the luminance signal of each block, a parameterQQP_(chroma)(i, j) is calculated by adding the weighting array W(i, j)to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal of each block, andweighted dequantization is performed using the resultant parameterQQP_(luma)(i, j) and the resultant parameter QQP_(chroma)(i, j).

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds a predetermined value QQP_(chroma) _(—) _(max), the weighteddequantization may be performed using the predetermined valueQQP_(chroma) _(—) _(max) as the parameter QQP_(chroma)(i, j).

In the first image information decoding method/apparatus, whencompressed image information is given which has been coded such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship were preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization was performed in accordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

the dequantization is performed in the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient, whereinwhen the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max), a commonration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{{chroma}\;\_\;\max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{{chroma}\;\_\;\max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{{chroma}\;\_\;\max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma _ max )) = round(A(QQP_(chroma _ max )) × r^(QQP_(chroma)(i, j) − QQP_(chroma _ max )))where round( ) denotes a round-into-integer function, and thedequantization is performed in accordance with the following formulaK′=LEVEL×B(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))where LEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—)_(max))+f×2^(m))/2^(m).

According to an aspect of the present invention, there is provided asecond image information decoding method/apparatus for decoding an inputimage signal which has been coded via a process including the steps ofdividing an input image signal into first blocks, performing a firstorthogonal transform on the first blocks on a block-by-block basis,forming second blocks including only DC components of orthogonaltransform coefficients obtained via the first orthogonal transform, andperforming a second orthogonal transform on the second blocks; andquantizing the coefficients of AC components obtained via the firstorthogonal transform and the coefficients of DC components obtained viathe second orthogonal transform such that the coefficients of the ACcomponents obtained via the orthogonal transform were weighteddifferently from the coefficients of the DC components obtained via thesecond orthogonal transform, wherein the decoding process includes thestep of dequantizing the quantized coefficients of AC components and thecoefficients of DC components quantized after completion of the secondorthogonal transform such that the quantized coefficients of ACcomponents and the coefficients of DC components are weighteddifferently by amounts corresponding to the weights employed in thequantization.

In this second image information decoding method/apparatus, as describedabove, when compressed image information is given which has beenquantized such that coefficients of DC components obtained via the firstorthogonal transform were extracted, and the second orthogonal transformwas performed on the extracted coefficients, and the coefficients of ACcomponents obtained via the first orthogonal transform and thecoefficients of DC components obtained via the second orthogonaltransform were quantized in weighted fashion such that the coefficientsof AC components were weighted differently from the coefficients of DCcomponents, the dequantization of the given image information may beperformed such that the quantized coefficients of AC components and thecoefficients of DC components quantized after being subjected to thesecond orthogonal transform are respectively dequantized with differentweights corresponding to the weights employed in the quantization.

Furthermore, in the second image information decoding method/apparatus,the dequantization of the coefficients of the AC components may beperformed using, as the parameter QP, a parameter QP_(luma) for aluminance signal and a parameter QP_(chroma) for a color differencesignal, and the dequantization of the coefficients of the DC componentsmay be performed using, as the parameter QQP, a parameter QQP_(luma)(i,j) for the luminance signal and a parameter QQP_(chroma)(i, j) for thecolor difference signal, wherein the parameter QQP_(luma)(i, j) isobtained by adding a weighting array W(i, j) as the parameter X to thearray of the parameter QP_(luma) corresponding to the respectivecomponents of the luminance signal of each block, and the parameterQQP_(chroma)(i, j) is obtained by adding the array W(i, j) as theparameter X to the array of the parameter QP_(chroma) corresponding tothe chroma respective components of the color difference signal of eachblock.

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max), thedequantization of the coefficients of DC components may be performedusing the predetermined value QQP_(chroma) _(—) _(max) as the parameterQQP_(chroma)(i, j).

In the second image information decoding method/apparatus, whencompressed image information is given which has been coded such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship were preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization of the coefficients of AC components was performed inaccordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

the dequantization of the coefficients of AC components is performed inthe following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient, whereinwhen the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max), a commonration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{chroma\_ max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{chroma\_ max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{chroma\_ max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma_max)) = round(A(QQP_(chroma_max)) × r^(QQP_(chroma)(i, j) − QQP_(chroma_max)))

and the dequantization of the coefficients of DC components is performedin accordance with the following formulaK′=LEVEL×B(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))where LEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—)_(max))f×2^(m))/2^(m).

The first image information decoding apparatus may be such an imageinformation decoding apparatus which decodes by performingdequantization and an inverse orthogonal transform on given compressedimage information which has been coded via a process including the stepsof dividing an input image signal into blocks, performing an orthogonaltransform on the blocks on a block-by-block basis, and quantizingresultant orthogonal transform coefficients, wherein the imageinformation decoding apparatus includes dequantization means forperforming the dequantization such that weighted dequantization isperformed on each component of the quantized coefficients by means of anaddition operation on a parameter QP specifying one of elements of aseries of numbers arranged in accordance with a predetermined rule incorrespondence with quantization step sizes.

In the first image information decoding apparatus, an array B(QP)consisting of elements having values which increase or decrease by β%with increasing of the value of the parameter QP by 1 may be used as thesequence of numbers corresponding to the quantization step sizes, andthe dequantization may be performed by multiplying the quantizedcoefficients by the values of the array B(QP).

In the first image information decoding apparatus, when the parameter QPexceeds an upper limit or a lower limit, the array B(QP) may be extendedso as to have an extended value or values determined on the basis of theincreasing or decreasing ratio of the original array B(QP), and theextended value or values of the B(QP) may be used for the exceedingvalue or values of the parameter QP.

That is, in the first image information decoding apparatus, thedequantization is performed such that the quantized coefficient ismultiplied by the value of the array B(QP), wherein QP is a parameterspecifying one of elements of a series of numbers arranged in accordancewith a predetermined rule in correspondence with quantization stepsizes, and the value of the array B(QP) increases or decreases by β%with increasing of the value of the parameter QP by 1.

When the parameter QP exceeds an upper limit or a lower limit, the arrayB(QP) may be extended so as to have an extended value or valuesdetermined on the basis of the increasing or decreasing ratio of theoriginal array B(QP), and the extended value or values of the B(QP) maybe used for the exceeding value or values of the parameter QP.

The parameter QP may include a parameter QP_(luma) applied to aluminance signal and a parameter QP_(chroma) applied to a colordifference signal, and the dequantization means may include firstcalculation means and second calculation means wherein the firstcalculation means calculates a parameter QQP_(luma)(i, j) by adding aweighting array W(i, j) to the array of the parameter QP_(luma)corresponding to the respective components of the luminance signal ofeach block, and the second calculation means calculates a parameterQQP_(chroma)(i, j) by adding the weighting array W(i, j) to the array ofthe parameter QP_(chroma) corresponding to the respective components ofthe color difference signal of each block, and wherein thedequantization means performs weighted dequantization using theparameter QQP_(luma)(i, j) calculated by the first calculation means andthe parameter QQP_(chroma)(i, j) calculated by the second calculationmeans.

When the parameter QQP_(chroma)(i, j) calculated by the secondcalculation means exceeds a predetermined value QQP_(chroma) _(—)_(max), the dequantization means may perform weighted dequantizationusing the predetermined value QQP_(chroma) _(—) _(max) as the parameterQQP_(chroma)(i, j).

In the first image information decoding apparatus, when compressed imageinformation is given which has been coded such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship were preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization was performed in accordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

the dequantization means may perform dequantization in accordance withthe following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient, whereinwhen the parameter QQP_(chroma)(i, j) calculated by the secondcalculation means exceeds the predetermined value on QQP_(chroma) _(—)_(max), the dequantization means may dequantization such that a commonration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{chroma\_ max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{chroma\_ max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{chroma\_ max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma_max)) = round(A(QQP_(chroma_max)) × r^(QQP_(chroma)(i, j) − QQP_(chroma_max)))where round( ) denotes a round-into-integer function, and thedequantization is performed in accordance with the following formulaK′=LEVEL×B(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))where LEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—)_(max))+f×2^(m))/2^(m).

The second image information decoding apparatus may be such an imageinformation decoding apparatus for decoding an input image signal whichhas been coded via a process including the steps of dividing an inputimage signal into first blocks, performing a first orthogonal transformon the first blocks on a block-by-block basis, forming second blocksincluding only DC components of orthogonal transform coefficientsobtained via the first orthogonal transform, and performing a secondorthogonal transform on the second blocks; and quantizing thecoefficients of AC components obtained via the first orthogonaltransform and the coefficients of DC components obtained via the secondorthogonal transform such that the coefficients of the AC componentsobtained via the first orthogonal transform were weighted differentlyfrom the coefficients of the DC components obtained via the secondorthogonal transform, wherein the apparatus includes dequantizationmeans for dequantizing the quantized coefficients of AC components andthe coefficients of DC components quantized after completion of thesecond orthogonal transform such that the quantized coefficients of ACcomponents and the coefficients of DC components are weighteddifferently by amounts corresponding to the weights employed in thequantization.

In the second image information decoding apparatus, when compressedimage information is given which has been quantized such thatcoefficients of DC components obtained via the first orthogonaltransform were extracted, and the second orthogonal transform wasperformed on the extracted coefficients, and the coefficients of ACcomponents obtained via the first orthogonal transform and thecoefficients of DC components obtained via the second orthogonaltransform were quantized in weighted fashion such that the coefficientsof AC components were weighted differently from the coefficients of DCcomponents, the dequantization of the given image information may beperformed such that the quantized coefficients of AC components and thecoefficients of DC components quantized after being subjected to thesecond orthogonal transform are respectively dequantized with differentweights corresponding to the weights employed in the quantization.

Furthermore, in the second image information decoding apparatus, thedequantization means may dequantize the coefficients of the ACcomponents using, as the parameter QP, a parameter QP_(luma) for aluminance signal and a parameter QP_(chroma) for a color differencesignal, wherein the second image information decoding apparatus mayfurther include first calculation means and second calculation means,the first calculation means serving to calculate a parameterQQP_(luma)(i, j) as the parameter QQP to be applied to the luminancesignal by adding a weighting array W(i, j) as the parameter X to thearray of the parameter QP_(luma) corresponding to the respectivecomponents of the luminance signal of each block, the second calculationmeans serving to calculate a parameter QQP_(chroma)(i, j) as theparameter QQP to be applied to the color difference signal by adding thearray W(i, j) as the parameter X to the array of the parameterQP_(chroma) corresponding to the respective components of the luminancesignal of each block, and wherein the dequantization means performsweighted dequantization using the parameter QQP_(luma)(i, j) calculatedby the first calculation means and the parameter QQP_(chroma)(i, j)calculated by the second calculation means.

When the parameter QQP_(chroma)(i, j) calculated by the secondcalculation means exceeds a predetermined value QQP_(chroma) _(—)_(max), the dequantization means may perform weighted dequantizationusing the predetermined value QQP_(chroma) _(—) _(max) as the parameterQQP_(chroma)(i, j).

In the second image information decoding apparatus, when compressedimage information is given which has been coded such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship were preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization of the coefficients of AC components was performed inaccordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

the dequantization means may perform dequantization of the coefficientsof AC components in the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient, whereinwhen the parameter QQP_(chroma)(i, j) calculated by the secondcalculation means exceeds the predetermined value QQP_(chroma) _(—)_(max), the dequantization means may perform dequantization such that acommon ration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{chroma\_ max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{chroma\_ max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{chroma\_ max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma_max)) = round(A(QQP_(chroma_max)) × r^(QQP_(chroma)(i, j) − QQP_(chroma_max)))where round( ) denotes a round-into-integer function,

and the dequantization of the coefficients of DC components is performedin accordance with the following formulaK′=LEVEL×B(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))where LEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—)_(max))+f×2^(m))/2^(m).

According to an aspect of the present invention, there is provided afirst image information coding and transmitting system comprising: animage signal coder for producing compressed image information bydividing an input image signal into blocks, performing an orthogonaltransform on the blocks on a block-by-block basis, and quantizingresultant orthogonal transform coefficient and also producing headerinformation; and a multiplex packetizer for, when the compressed imageinformation and the header information are received from the imagesignal coder, multiplexing the compressed image information and theheader information in accordance with a predetermined method andtransmitting the resultant multiplexed information in the form ofpackets, wherein when the image signal coder quantizes orthogonaltransform coefficients obtained via the orthogonal transform, the imagesignal coder performs weighted quantization on each component of theorthogonal transform coefficients by means of an addition operation on aparameter QP specifying one of elements of a series of numbers arrangedin accordance with a predetermined rule in correspondence withquantization step sizes; and the multiplex packetizer multiplexesinformation associated with the quantization weighting together with theheader information and packetizes the multiplexed information.

In this first image information coding and transmitting system, theparameter QP may include a parameter QP_(luma) applied to a luminancesignal and a parameter QP_(chroma) applied to a color difference signal;and the image signal coder may perform weighted quantization such that aparameter QQP_(luma)(i, j) is calculated by adding a weighting arrayW(i, j) to the array of the parameter QP_(luma) corresponding to therespective components of the luminance signal of each block, a parameterQQP_(chroma)(i, j) is calculated by adding the weighting array W(i, j)to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal of each block, andweighted quantization is performed using the resultant parameterQQP_(luma)(i, j) and the resultant parameter QQP_(chroma)(i, j).

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds a predetermined value QQP_(chroma) _(—) _(max), the image signalcoder may perform weighted quantization using the predetermined valueQQP_(chroma) _(—) _(max) as the parameter QQP_(chroma)(i, j).

The image information coding apparatus may perform coding such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship are preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)

where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output, dequantization corresponding to thequantization is to be performed in accordance with the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient, whereinwhen the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max), a commonration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{chroma\_ max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{chroma\_ max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{chroma\_ max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma_max)) = round(A(QQP_(chroma_max)) × r^(QQP_(chroma)(i, j) − QQP_(chroma_max)))where round( ) denotes a round-into-integer function, and

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))f×2^(m))/2^(m).

As described above, the first image information coding and transmittingsystem includes an image signal coder for producing compressed imageinformation by dividing an input image signal into blocks, performing anorthogonal transform on the blocks on a block-by-block basis, andquantizing resultant orthogonal transform coefficient and also producingheader information; and a multiplex packetizer for, when the compressedimage information and the header information are received from the imagesignal coder, multiplexing the compressed image information and theheader information in accordance with a predetermined method andtransmitting the resultant multiplexed information in the form ofpackets.

In this first image information coding and transmitting system, asdescribed above, when the image signal coder quantizes orthogonaltransform coefficients obtained via the orthogonal transform, the imagesignal coder performs weighted quantization on each component of theorthogonal transform coefficients by means of an addition operation on aparameter QP specifying one of elements of a series of numbers arrangedin accordance with a predetermined rule in correspondence withquantization step sizes; and the multiplex packetizer multiplexesinformation associated with the quantization weighting together with theheader information and packetizes the multiplexed information.

According to an aspect of the present invention, there is provided asecond image information coding and transmitting system comprising animage signal coder for producing compressed image information bydividing an input image signal into blocks, performing an orthogonaltransform on the blocks on a block-by-block basis, and quantizingresultant orthogonal transform coefficient and also producing headerinformation; and a multiplex packetizer for, when the compressed imageinformation and the header information are received from the imagesignal coder, multiplexing the compressed image information and theheader information in accordance with a predetermined method andtransmitting the resultant multiplexed information in the form ofpackets, wherein the multiplex packetizer adds at least the headerinformation to each access unit, at the beginning thereof, of thecompressed image information.

In this second image information coding and transmitting system, theparameter QP may include a parameter QP_(luma) applied to a luminancesignal and a parameter QP_(chroma) applied to a color difference signal,and the image signal coder may perform weighted quantization such that aparameter QQP_(luma)(i, j) is calculated by adding a weighting arrayW(i, j) to the array of the parameter QP_(luma) corresponding to therespective components of the luminance signal of each block, a parameterQQP_(chroma)(i, j) is calculated by adding the weighting array W(i, j)to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal of each block, andweighted quantization is performed using the resultant parameterQQP_(luma)(i, j) and the resultant parameter QQP_(chroma)(i, j).

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds a predetermined value QQP_(chroma) _(—) _(max), the image signalcoder may perform weighted quantization using the predetermined valueQQP_(chroma) _(—) _(max) as the parameter QQP_(chroma)(i, j).

The image information coding apparatus may perform coding such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship are preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

dequantization corresponding to the quantization is to be performed inaccordance with the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient,

wherein when the parameter QQP_(chroma)(i, j) obtained via thecalculation exceeds the predetermined value QQP_(chroma) _(—) _(max), acommon ration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{chroma\_ max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{chroma\_ max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{chroma\_ max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma_max)) = round(A(QQP_(chroma_max)) × r^(QQP_(chroma)(i, j) − QQP_(chroma_max)))where round( ) denotes a round-into-integer function, and

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max))+f×2^(m))/2^(m).

As described above, the second image information coding and transmittingsystem includes an image signal coder for producing compressed imageinformation by dividing an input image signal into blocks, performing anorthogonal transform on the blocks on a block-by-block basis, andquantizing resultant orthogonal transform coefficient and also producingheader information; and a multiplex packetizer for, when the compressedimage information and the header information are received from the imagesignal coder, multiplexing the compressed image information and theheader information in accordance with a predetermined method andtransmitting the resultant multiplexed information in the form ofpackets, wherein the multiplex packetizer adds at least the headerinformation to each access unit, at the beginning thereof, of thecompressed image information.

According to an aspect of the present invention, there is provided athird image information coding and transmitting system comprising animage signal coder for producing compressed image information bydividing an input image signal into blocks, performing an orthogonaltransform on the blocks on a block-by-block basis, and quantizingresultant orthogonal transform coefficient and also producing headerinformation; and a multiplex packetizer for, when the compressed imageinformation and the header information are received from the imagesignal coder, multiplexing the compressed image information and theheader information in accordance with a predetermined method andtransmitting the resultant multiplexed information in the form ofpackets, wherein when the image signal coder quantizes orthogonaltransform coefficients obtained via the orthogonal transform, the imagesignal coder performs weighted quantization on each component of theorthogonal transform coefficients by means of an addition operation on aparameter QP specifying one of elements of a series of numbers arrangedin accordance with a predetermined rule in correspondence withquantization step sizes; and the multiplex packetizer multiplexesinformation associated with the quantization weighting together with theheader information, packetizing the resultant multiplexed informationseparately from the compressed image information, and transmits theresultant packetized information and the compressed image informationseparately via different channels.

In this third image information coding and transmitting system, theparameter QP may include a parameter QP_(luma) applied to a luminancesignal and a parameter QP_(chroma) applied to a color difference signal;and the image signal coder may perform quantization such that aparameter QQP_(luma)(i, j) is calculated by adding a weighting arrayW(i, j) to the array of the parameter QP_(luma) corresponding to therespective components of the luminance signal of each block, a parameterQQP_(chroma)(i, j) is calculated by adding the weighting array W(i, j)to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal of each block, andweighted quantization is performed using the resultant parameterQQP_(luma)(i, j) and the resultant parameter QQP_(chroma)(i, j).

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds a predetermined value QQP_(chroma) _(—) _(max), the image signalcoder may perform weighted quantization using the predetermined valueQQP_(chroma) _(—) _(max) as the parameter QQP_(chroma)(i, j).

The image information coding apparatus may perform coding such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship are preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)

dequantization corresponding to the quantization is to be performed inaccordance with the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient, whereinwhen the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max), a commonration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{chroma\_ max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{chroma\_ max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{chroma\_ max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma_max)) = round(A(QQP_(chroma_max)) × r^(QQP_(chroma)(i, j) − QQP_(chroma_max)))where round( ) denotes a round-into-integer function, and

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))+f×2^(m))/2^(m).

As described above, the third image information coding and transmittingsystem includes an image signal coder for producing compressed imageinformation by dividing an input image signal into blocks, performing anorthogonal transform on the blocks on a block-by-block basis, andquantizing resultant orthogonal transform coefficient and also producingheader information; and a multiplex packetizer for, when the compressedimage information and the header information are received from the imagesignal coder, multiplexing the compressed image information and theheader information in accordance with a predetermined method andtransmitting the resultant multiplexed information in the form ofpackets, wherein when the image signal coder quantizes orthogonaltransform coefficients obtained via the orthogonal transform, the imagesignal coder performs weighted quantization on each component of theorthogonal transform coefficients by means of an addition operation on aparameter QP specifying one of elements of a series of numbers arrangedin accordance with a predetermined rule in correspondence withquantization step sizes; and the multiplex packetizer multiplexesinformation associated with the quantization weighting together with theheader information, packetizing the resultant multiplexed informationseparately from the compressed image information, and transmits theresultant packetized information and the compressed image informationseparately via different channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of a construction of animage information coding apparatus according to an embodiment of thepresent invention;

FIG. 2 is a block diagram showing an example of a construction of animage information decoding apparatus according to an embodiment of thepresent invention;

FIG. 3 is a diagram showing a default weighting matrix applied to intramacroblocks or luminance signals, stored in a weighter of the imageinformation coding apparatus shown in FIG. 1;

FIG. 4 is a diagram showing a default weighting matrix applied tonon-intra macroblocks or color difference signals, stored in theweighter of the image information coding apparatus shown in FIG. 1;

FIG. 5 is a table indicating the number of bits necessary to representthe quantized discrete cosine coefficients, for a case in which therange of a parameter used in quantization or dequantization is extendedto −8;

FIG. 6 is a diagram showing an example of a syntax for embeddinginformation associated with extended quantization step sizes intocompressed image information;

FIG. 7 is a table indicating the correspondence between parameters usedin dequantization and quantizer_range included in compressed imageinformation;

FIG. 8 is a diagram showing an example of a syntax for embeddinginformation associated with a weighting matrix applied to DC componentsinto compressed image information, for a case in which each component iscoded with accuracy of 4 bits;

FIG. 9 is a diagram showing an example of a syntax for embeddinginformation associated with a weighting matrix applied to DC componentsinto compressed image information, for a case in which each component isUVLC-coded;

FIG. 10 is a diagram showing an example of a syntax for embedding, on aGOP-by-GOP basis, information associated with a weighting matrix appliedto DC components into compressed image information;

FIG. 11 is a diagram showing an example of a syntax for embeddinginformation associated with a weighting matrix into compressed imageinformation only when the weighting matrix is to be changed, whereineach component is coded with accuracy of 4 bits;

FIG. 12 is a diagram showing an example of a syntax for embeddinginformation associated with a weighting matrix into compressed imageinformation only when the weighting matrix is to be changed, whereineach component is coded by means of UVLC;

FIG. 13 is a block diagram showing an example of a construction of animage information coding and transmitting system according the presentinvention;

FIG. 14 is a diagram showing an example of a syntax for embeddinginformation associated with a weighting parameter applied to DCcomponents into compressed image information, for a case in which theweighting parameter is embedded on a GOP-by-GOP basis;

FIG. 15 is a diagram showing an example of a syntax for embeddinginformation associated with a weighting parameter applied to DCcomponents into compressed image information, for a case in which theweighting parameter is embedded on a picture-by-picture basis;

FIG. 16 is a block diagram showing another example of a construction ofan image information coding apparatus according to the presentinvention;

FIG. 17 is a block diagram showing another example of a construction ofan image information decoding apparatus according to the presentinvention;

FIG. 18 is a block diagram showing another example of a construction ofan image information coding apparatus or an image information codingapparatus according to the present invention;

FIG. 19 is a block diagram showing an example of a construction of animage information coding apparatus according to a conventionaltechnique;

FIG. 20 is a block diagram showing an example of a construction of animage information decoding apparatus according to a conventionaltechnique;

FIG. 21 is a table showing relationships among intra_dc_precision, bitaccuracy, dequantization coefficient, and predicted DC reset value,according to the MPEG2 standard;

FIG. 22 is a diagram showing default values of a quantization matrix tobe applied to intra macroblocks, according to the MPEG2 standard;

FIG. 23 is a diagram showing default values of a quantization matrix tobe applied to inter macroblocks, according to the MPEG2 standard;

FIG. 24 is a diagram showing a quantization matrix to be applied tonon-intra macroblocks, according to MPEG2 Test Model 5; and

FIG. 25 is a table showing relationships among parameters,quantiser_scale, q_scale_type (set on a picture-by-picture basis, andquantiser_scale_code (set on a macroblock-by-macroblock basis) accordingto the MPEG2 standard.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is described in further detail below withreference to specific embodiments in conjunction with the accompanyingdrawings.

First Embodiment

As a first embodiment of the present invention, an image signal coderfor producing compressed image information by dividing an input imagesignal into blocks, performing an orthogonal transform on the blocks ona block-by-block basis, and quantizing resultant orthogonal transformcoefficients, and an image signal decoder for decoding coded imageinformation by dequantizing it and performing an inverse transform aredescribed.

In the image information coding apparatus and the image informationdecoding apparatus according to the present embodiment, as will bedescribed in detail later, weighting is performed on a parameterspecifying one of elements of a sequence of numbers arranged inaccordance with a predetermined rule in correspondence to quantizationstep sizes thereby making it possible to use greater quantization stepsizes in quantizing orthogonal transform coefficients in a highfrequency range in which the great quantization step sizes does notresult in significant visually-perceptible degradation, than in a lowfrequency range in which degradation is easily perceptible, and alsomaking it possible to prevent a spurious contour line from being createdin an image including a part with gradually varying pixel values

First, referring to FIG. 1, an image information coding apparatusaccording to the first embodiment of the present invention is described.

As shown in FIG. 1, the image information coding apparatus 10 accordingto the first embodiment of the present invention includes ananalog-to-digital converter 11, a frame rearrangement buffer 12, anadder 13, an orthogonal transformer 14, a quantizer 15, a weighter 16, alossless coder 17, a storage buffer 18, a dequantizer 19, a weighter 20,an inverse orthogonal transformer 21, a frame memory 22, a motionprediction compensator 23, and a rate controller 24.

The operation of the image information coding apparatus 10 is describedbelow.

In FIG. 1, the analog-to-digital converter 11 converts an input imagesignal into a digital signal. The frame rearrangement buffer 12rearranges frames depending on the GOP (Group of Pictures) structure ofthe compressed image information output from the image informationcoding apparatus 10.

When the frame rearrangement buffer 12 receives a frame to beintra-coded, the frame rearrangement buffer 12 supplies the imageinformation of the entire frame to the orthogonal transformer 14. Theorthogonal transformer 14 performs an orthogonal transform such as adiscrete cosine transform or a Karhunen-Loeve transform on the imageinformation and supplies resultant transform coefficients to thequantizer 15.

The quantizer 15 quantizes the transform coefficients received from theorthogonal transformer 14. In this process, as will be described later,the weighter 16 of the quantizer 15 performs weighting on a parameterspecifying one of elements of a sequence of numbers arranged inaccordance with a predetermined rule in correspondence to quantizationstep sizes, for each component of the transform coefficients.

The lossless coder 17 performs lossless coding by means of variablelength coding or arithmetic coding on the quantized transformcoefficients and supplies the resultant coded transform coefficients tothe storage buffer 18. The storage buffer 18 stores the received codedtransform coefficients. The coded transform coefficients are output ascompressed image information from the storage buffer 18.

The behavior of the quantizer 15 is controlled by the rate controller24. The quantizer 15 also supplies the quantized transform coefficientsto the dequantizer 19. The dequantizer 19 dequantizes the receivedtransform coefficients. In this process, as will be described later, theweighter 20 of the dequantizer 19 performs weighting on a parameterspecifying one of elements of a sequence of numbers arranged inaccordance with a predetermined rule in correspondence to quantizationstep sizes, for each component of the quantized transform coefficients.

The inverse orthogonal transformer 21 performs an inverse orthogonaltransform on the dequantized transform coefficients thereby producingdecoded image information and stores the resultant decoded imageinformation into the frame memory 22.

On the other hand, image information of those frames to beinterframe-coded is supplied from the frame rearrangement buffer 12 tothe motion prediction compensator 23. At the same time, the motionprediction compensator 23 reads image information to be referred to fromthe frame memory 22 and performs motion prediction compensation toproduce reference image information.

The motion prediction compensator 23 supplies the reference imageinformation to the adder 13. The adder 13 produces a difference signalindicating the difference between the image information and thereference image information. At the same time, the motion predictioncompensator 23 also supplies the motion vector information to thelossless coder 17.

The lossless coder 17 performs lossless coding by means of variablelength coding or arithmetic coding on the motion vector informationthereby producing information to be put in a header of the compressedimage information. The other processes are performed in a similar mannerto compressed image information to be intra-coded, and thus they are notdescribed herein in further detail.

Now, referring to FIG. 2, an image information decoding apparatusaccording to the first embodiment of the present invention is described.

As shown in FIG. 2, the image information decoding apparatus 30according to the first embodiment of the present invention includes astorage buffer 31, a lossless decoder 32, a dequantizer 33, a weighter34, an inverse orthogonal transformer 35, an adder 36, a framerearrangement buffer 37, a digital-to-analog converter 38, a motionprediction compensator 39, and frame memory 40.

The operation of the image information decoding apparatus 30 isdescribed below.

In FIG. 2, compressed image information input to the storage buffer 31is transferred to the lossless decoder 32 after being temporarily storedin the storage buffer 31. The lossless decoder 32 decodes the receivedcompressed image information by means of variable length decoding orarithmetic decoding in accordance with the format of the compressedimage information and supplies the resultant quantized transformcoefficients to the dequantizer 33. In a case in which the frame beingprocessed is an interframe-coded frame, the lossless decoder 32 alsodecodes the motion vector information described in the header of thecompressed image information and supplies the resultant decodedinformation to the motion prediction compensator 39.

The dequantizer 33 dequantizes the quantized transform coefficientssupplied from the lossless decoder 32 and supplies the resultanttransform coefficients to the inverse orthogonal transformer 35. In thisprocess, as will be described later, the weighter 34 of the dequantizer33 performs weighting on a parameter specifying one of elements of asequence of numbers arranged in accordance with a predetermined rule incorrespondence to quantization step sizes, for each component of thequantized transform coefficients. The inverse orthogonal transformer 35performs an inverse orthogonal transform such as an inverse discretecosine transform or an inverse Karhunen-Loeve transform on the transformcoefficients in accordance with the predetermined format of thecompressed image information.

In a case in which the frame being processed is an intraframe-codedframe, the inverse orthogonal transformer 35 supplies the resultantimage information to the frame rearrangement buffer 37. The framerearrangement buffer 37 temporarily stores the received imageinformation and supplies it the digital-to-analog converter 38 after thetemporary storage. The digital-to-analog converter 38 converts thereceived image information into analog form and outputs the resultantimage information in the analog form.

On the other hand, in a case in which the frame being processed is aninterframe-coded frame, the motion prediction compensator 39 produces anreference image on the basis of the motion vector information subjectedto the lossless decoding process and the image information stored in theframe memory 40. The adder 36 adds the received reference image to theoutput of the inverse orthogonal transformer 35. The other processes areperformed in a similar manner to the intra-coded frame, and thus theyare not described herein in further detail.

The details of the weighter 16 and the weighter 20 of the imageinformation coding apparatus 10 (FIG. 1) and the weighter 34 of theimage information decoding apparatus 30 (FIG. 2) are described below.

As described above, when the quantizer 15 (FIG. 1), the dequantizer 19(FIG. 1), and the dequantizer 33 (FIG. 2) perform quantization ordequantization, the weighter 16, the weighter 20, and the weighter 34disposed in the respective quantizer or dequantizers perform weightingon the parameter specifying one of elements of the sequence of numbersarranged in the predetermined rule in correspondence with thequantization step sizes.

The weighting described above makes it possible to use greaterquantization step sizes in quantizing orthogonal transform coefficientsin the high frequency range in which the great quantization step sizesdoes not result in significant visually-perceptible degradation, than inthe low frequency range in which degradation is easily perceptible.

The weighting process is described in further detail below. Because theweighter 16, the weighter 20, and the weighter 34 operate in a similarmanner, the operation is described herein only for the weighter 16.

The weighter 16 has information indicating default values of an arrayW_(intra)(i, j) (i, j)=0, 1, 2, 3) to be applied to intra macroblocks. Aspecific example of a set of default values is shown in FIG. 3.

Similarly, the weighter 16 has information indicating default values ofan array W_(inter)(i, j) (i, j=0, 1, 2, 3) to be applied to intermacroblocks. A specific example of a set of default values is shown inFIG. 4.

The values shown in FIG. 3 may be employed as default values of an arrayW_(luma)(i, j) (i, j=0, 1, 2, 3) to be applied to a luminance signal,and the values shown in FIG. 4 may be employed as default values of anarray W_(chroma)(i, j) (i, j=0, 1, 2, 3) to be applied to a colordifference signal.

Because processes associated with the arrays W_(intra)(i, j)W_(inter)(i, j), W_(luma)(i, j), and W_(chroma)(i, j) are similar toeach other, those arrays will be referred to simply as W(i, j) unlessdistinction is necessary.

Note that the values of the arrays W_(intra)(i, j), W_(inter)(i, j), thearrays W_(luma)(i, j), and W_(chroma)(i, j) are not limited to defaultvalues shown in FIG. 3 or FIG. 4, but a user may set the values on apicture-by-picture basis. When the values of W(i, j) are set on thepicture-by-picture basis, the values may be directly embedded incompressed image information, or the original values may be convertedinto a compressed form by means of conversion into difference values orby means of lossless coding such as variable length coding or arithmeticcoding and resultant compressed data may be embedded.

In the weighter 16, a parameter QQP(i, j) is defined, according toequation (10), for each component of 4×4 discrete cosine coefficients onthe basis of the parameter QP used in macroblock-by-macroblockquantization, stored in compressed image information.QQP(i,j)=QP+W(i,j)  (10)

In the present embodiment, quantization/dequantization is performed oneach component in a similar manner as defined in the H.26L standarddescribed earlier. However, arrays A(QP) and B(QP) employed in the H.26Lstandard are replaced with A(QQP(i, j)) and B(QQP(i, j)), respectively.

The dynamic range of QP is 0 to 31. However, there is a possibility thatthe value of QQP(i, j) in equation (10) exceeds 31. In such a case, theprocess is performed according to one of methods described below.

In a first method, when the value of QQP(i, j) exceeds 31, the value isreplaced by 31 such that QQP(i, j)=31. In the second method, the QQP(i,j) is allowed to have a value greater than 31, and values of A(QQP(i,j)) and B(QQP(i, j)) are defined in accordance with equations (11) and(12), respectively.

$\begin{matrix}{{A\left( {{{QQP}\left( {i,j} \right)} > 31} \right)} = {{round}\left( \frac{17}{1.12^{{{QQP}{({i,j})}} - 31}} \right)}} & (11) \\{{B\left( {{{QQP}\left( {i,j} \right)} > 31} \right)} = {{round}\left( {141533 \times 1.12^{{{QQP}{({i,j})}} - 31}} \right)}} & (12)\end{matrix}$

In equations (11) and (12), round( ) denotes a round-into-integerfunction.

A(QQP(i, j)) and B(QQP(i, j)) determined in the above-described mannersatisfy a relationship represented by equation (13) corresponding toequation (7).A(QQP(i,j))×B(QQP(i,j))×676²=2⁴⁰  (13).

In quantization/dequantization, use of A(QQP(i, j)) and B(QQP(i, j)) forQQP(i, j)>31 makes it possible to achieve high-efficient compression atlow bit rates.

In the quantization/dequantization of the luminance signal, the dynamicrange may be expanded according to the second method described above,while clipping according to the first method may be employed for thecolor difference signal.

For QQP(i, j)<0, A(QQP(i, j)) and B(QQP(i, j)) are calculated accordingto equations (14) and (15), respectively, quantization/dequantization isperformed in a similar manner as is defined in the H.26L standard usingA(QQP(i, j)) or B(QQP(i, j)).

$\begin{matrix}{{A\left( {{{QQP}\left( {i,j} \right)} < 0} \right)} = {{round}\left( {620 \times 1.12^{- {{QQP}{({i,j})}}}} \right)}} & (14) \\{{B\left( {{{QQP}\left( {i,j} \right)} < 0} \right)} = {{round}\left( \frac{3881}{1.12^{- {{QQP}{({i,j})}}}} \right)}} & (15)\end{matrix}$

Use of A(QQP(i, j)) and B(QQP(i, j)) determined in the above-describedmanner makes it possible to prevent degradation in image quality due tocreation of a spurious contour line in an image including a part whosepixel value varies gradually.

In the image information coding in accordance with H.26L, creation ofsuch a spurious contour line results from insufficient accuracy of (0,0), (0, 1) and (1, 0)-components of 4×4 discrete cosine transformcoefficients.

In the present embodiment, the above problem is avoided by employing aweighting matrix given by equation (16) as W(i, j).

$\begin{matrix}\begin{bmatrix}{- 8} & {- 6} & 0 & 0 \\{- 6} & 0 & 0 & 0 \\0 & 0 & 0 & 0 \\0 & 0 & 0 & 0\end{bmatrix} & (16)\end{matrix}$

The expansion of the dynamic range of A(QQP(i, j)) and B(QQP(i, j))using equations (14) and (15) may be performed only for intermacroblocks or only for luminance signal components.

The expansion according to equations (14) and (15) can cause indicesQQP(i, j) of A( ) and B( ) to become negative, which is undesirable insyntax of compressed image information.

The above problem can be avoided by employing new indices QQP′(i, j)given by equation (17) in quantization/dequantization, wherein QQP_(min)(<0) denotes a minimum value of QQP(i, j).QQP′(i,j)=QQP(i,j)−QQP _(min)  (17)

For example, if expansion according to equations (11), (12), (14), and(15) is performed so as to make it possible for QQP(i, j) to take avalue in the range from −3 to 34, QQP′(i, j) given by equation (17) cantake a value in the range from 0 to 37.

For a simple profile according to H.26L, a value in the range from 3 to34 may be employed while value in the range from 0 to 34 may be employedfor a complicated profile such as a 10-bit image.

An example of a manner of expanding the dynamic range of A(QQP(i, j))and B(QQP(i, j)) according to equations (11), (12), (14), and (15) isdescribed below.

Degradation in image quality due to creation of a spurious contour linein an image including a part having gradually varying pixel values canbe avoided if quantization accuracy as measured by a correspondingquantization scale used in nonlinear quantization according to the MPEG2standard is close to 1.

To meet the above requirement, the dynamic range of A(QQP(i, j)) andB(QQP(i, j)) may be expanded in the negative direction according toequations (14) and (15) as shown below.

A(QQP=−8 to 0): 1535, 1370, 1224, 1093, 976, 871, 777, 694, 620

B(QQP=−8 to 0): 1567, 1756, 1966, 2201, 2465, 2762, 3097, 3467, 3881

MPEG2-based quantization step sizes corresponding to the combination ofextended A(QQP(i, j)) and B(QQP(i, j)) are 1.0105, 1.1322, 1.2673,1.4192, 1.589, 1.7801, 1.9963, 1.235, and 2.5019.

Thus, accuracy as high as about 1 in quantization scale is obtained, andthus it becomes possible to prevent degradation in image quality due tocreation of a spurious contour line in an image including a part withgradually varying pixel values.

Herein, a measure, R(QQP(i, j)), indicating the operation accuracy ofthe above combination is introduced as shown in equation (18).R(QQP(i,j))=A(QQP(i,j))·B(QQP(i,j))·676²/2⁴⁰  (18)

The closer to 1.0 the value of R(QQP(i, j)), the smaller the operationerror. For the above-described combination of A(QQP(i, j)) and B(QQP(i,j)), R(QQP(i, j)) has values of 0.9997, 0.9999, 1.0001, 0.9998, 0.9999,1.0012, 1.0000, and 1.0001 for QQP(i, i) of −8 to 0, respectively, andthus the accuracy is high enough.

The dynamic ranges of A(QQP(i, j)) and B(QQP(i, j)) may be extended tothe positive direction on the basis of equations (11) and (12), as shownbelow.

A(QQP=31, . . . , 35): 17, 15, 13, 12, 11

B(QQP=31, . . . , 35): 141533, 160404, 185082, 200505, 218733

MPEG2-based quantization step sizes corresponding to the combination ofA(QQP(i, j)) and B(QQP(i, j)) extended in the above-described mannerwill be 91.2440, 103.4099, 119.3191, 129.2623, and 141.0135, and thushigh-efficiency compression can be achieved at low bit rates.

If R(QQP(i, j)) is calculated for the above combination of A(QQP(i, j))and B(QQP(i, j)) the resultant values of R are 1.0000, 1.0000, 1.0000,1.0000, and 1.0000 for QQP(i, j) of 31 to 35, respectively, and thus theaccuracy is high enough.

When the dynamic ranges of A(QQP(i, j)) and B(QQP(i, j)) are expandedusing the above-descried technique, the bit length of associated databecomes as follows.

For example, when QQP(i, j)=0, if an input pixel value or a differencevalue thereof has accuracy of 9, the maximum value of the quantizedorthogonal transform coefficients, LEVEL, is given as 408(=255×52²×620/2²⁰, and thus 10 bits are necessary to represent LEVEL.

FIG. 5 shows the number of bits necessary to represent the quantizedorthogonal transform coefficient LEVEL for QQP of −1 to −8.

FIG. 6 shows an example of a syntax for embedding information associatedwith the extended quantization step sizes into compressed imageinformation.

As can be seen from FIG. 7, quantizer_range shown in FIG. 6 is a flagindicating which range of values of QQP(i, j) extended according toequations (11), (12), (14), and (15) should be used in compressed imageinformation. When this flag has a value of 0,quantization/dequantization is performed in the same manner as definedin the current H.26L standard.

In the image information coding apparatus and the image informationdecoding apparatus according to the present invention, a defaultweighting matrix to applied to the luminance signal is defined byequation (19), and that applied to the color difference signals isdefined by equation (20).

$\begin{matrix}{{W_{intra}\left( {i,j} \right)} = \begin{pmatrix}8 & 9 & 10 & 11 \\9 & 10 & 11 & 12 \\10 & 11 & 12 & 13 \\11 & 12 & 13 & 14\end{pmatrix}} & (19) \\{{W_{{non}\text{-}{intra}}\left( {i,j} \right)} = \begin{pmatrix}8 & 8 & 8 & 8 \\8 & 8 & 8 & 8 \\8 & 8 & 8 & 8 \\8 & 8 & 8 & 8\end{pmatrix}} & (20)\end{matrix}$

The weighting matrices used in quantization/dequantization performed inthe image information coding apparatus or the image information decodingapparatus are not limited to the default matrices described above, butweighting matrices can be set by a user for each picture.

In FIG. 6, load_intra_quantiser_matrix, load_non_intra_quantiser_matrix,load_chroma_intra_quantiser_matrix, andload_chroma_non_intra_quantiser_matrix are 1-bit flags indicatingwhether a weighting matrix other than the default weighting matrixshould be used for the luminance and color difference signals in intramacroblocks and inter macroblocks, wherein the weighting matrix otherthan the default weighting matrix is used when the flag has a value of1.

For example, if load_intra_quantiser_matrix has a value of 1,information associated with 4×4 weighting matrix whose components areeach represented in 4 bits is described in followingintra_quantiser_matrix[16].

The length of each component is not limited to 4 bits as in the presentembodiment, but the length may be 8, 12, or another number of bits.

The information associated with intra_quantiser_matrix[16] may becompressed by means of conversion into difference values or by means oflossless coding such as variable length coding or arithmetic coding.

Although in the embodiment described above, the pixel value of inputimage information is represented in 8 bits, the above-describedexpansion may also be applied to image information whose pixel value isrepresented in a different number of bits, such as 10 bits.

In the image information coding apparatus 10 (FIG. 1) and the imageinformation decoding apparatus 30 (FIG. 2) according to the presentembodiment, as described above, weighted quantization/dequantization isachieved by performing weighting on the parameter specifying one ofelements of the sequence of numbers arranged in accordance with thepredetermined rule in correspondence to quantization step sizes, so thatgreater quantization step sizes are employed in quantization oforthogonal transform coefficients in the high frequency range in whichthe great quantization step sizes does not result in significantvisually-perceptible degradation, and smaller quantization step sizesare employed in the low frequency range in which degradation is easilyperceptible.

Furthermore, it also becomes possible to extend the dynamic range evenin the case in which the weighting causes the parameter to go out of thepredetermined range, thereby making it possible to prevent a spuriouscontour line from being created in an image including a part withgradually varying pixel values and also making it possible to performhigh-efficient compression at low bit rates.

Modifications of the first embodiment are described below.

First Modification

In the first embodiment described above, two arrays A(QP) and B(QP) aregiven in the form of tables.

Alternatively, two arrays A(QP) and B(QP) may be determined inaccordance with equations as described below.

For example, arrays A(QP) and B(QP) may be given by equations (21) and(22), respectively.A(QP)=A _(mantissa)(QP)·2^(A) ^(exponent) ^((QP))  (21)B(QP)=B _(mantissa)(QP)·2^(B) ^(exponent) ^((QP))  (22)

In the above equations ((21) and (22)), array A(QP) is set such that thevalues of elements thereof decrease by 12% with increasing of the valueof QP by 1, the values of elements of array A(QP) is approximatelyhalved each time the value of QP increases by 6. Thus, ifA_(mantissa(QP)) is defined for first six values of QP in equation (21),then array A(QP) can be extended such that any set of six elements areproduced by multiplying a previous set of six elements by ½ as shown inequation (23).

$\begin{matrix}{\mspace{79mu}{\left\{ {a_{1},a_{2},a_{3},a_{4},a_{5},a_{6}} \right\},\left\{ {{a_{7}\left( {= \frac{a_{1}}{2}} \right)},{a_{8}\left( {= \frac{a_{2}}{2}} \right)},{a_{9}\left( {= \frac{a_{3}}{2}} \right)},{a_{10}\left( {= \frac{a_{4}}{2}} \right)},{a_{11}\left( {= \frac{a_{5}}{2}} \right)},{a_{12}\left( {= \frac{a_{6}}{2}} \right)}} \right\},\ldots}} & (23)\end{matrix}$

Thus, the quantized output level LEVEL(i, j) of a coefficient f(i, j) isgiven by equation (24).LEVEL(i,j)=sign(f(i,j))((|f(i,j)|//2^(fdct) ^(—) ^(shift) ×A _(man)[QP%6]+qp_const)/2^(shift(QP))  (24)

Specific examples of parameters such as fdct_shift in equation (24) areshown in equations (25) to (30).fdct_shift=7  (25)Intra:qp_const=(1<<(20−A _(exp 0) +QP/6−fdct_shift))/3  (26)Inter:qp_const=(1<<(20−A _(exp 0) +QP/6−fdct_shift))/6  (27)A _(exp 0)=−5  (28)shift(QP)=20−A _(exp 0) +QP/6−fdct_shift  (29)intA _(man)[6]={20050, 18797, 15829, 14322, 12532, 11139}  (30)

Similarly, if array B(QP) is set such that the values of elementsthereof increase by 12% with increasing of QP by 1, the values ofelements of array B(QP) is approximately doubled each time the value ofQP increases by 6. Thus, if B_(mantissa(QP)) is defined for first sixvalues of QP in equation (22), then array B(QP) can be extended suchthat any set of six elements are produced by multiplying a previous setof six elements by 2 as shown in equation (31).{b ₁ ,b ₂ ,b ₃ ,b ₄ ,b ₅ ,b ₆ },{b ₇(=2b ₁),b ₈(=2b ₂),b ₉(=2b ₃),b₁₀(=2b ₄),b ₁₁(=2b ₅),b ₁₂(=2b ₆)},  (31)

Thus, the dequantized output f(i, j) of the quantized output levelLEVEL(i, j) is given by equation (32).f(i,j)=LEVEL(i,j)×B _(man)(QP%6)<<(QP/6)  (32)

Specific examples of B{exp 0} and intB_(man) are shown in equations (33)and (34), respectively.B _(exp 0)=6  (33)intB _(man)[6]={60, 64, 76, 84, 96, 108}  (34)

In the case in which arrays A(QP) and B(QP) are given by mathematicalexpressions, the same effects and advantages as those described abovecan be achieved by calculating QQP according to QQP(i, j)=QP+W(i, j) andreplacing QP in equations with QQP.

Second Modification

In H.26L (JVT Codec), 4×4-size orthogonal transform and quantization areperformed on 16 DC components of a luminance signal in a macroblock tobe intra-coded, and 2×2-size orthogonal transform and quantization areperformed on 4 DC components of color difference signals in themacroblock to be intra-coded. The orthogonal transform is not limited tothe discrete cosine transform employed in the present embodiment, butother orthogonal transforms such as an Hadamard transform may also beemployed.

In the quantization of DC components of the luminance signal and thecolor difference signal, a weighting matrix W(i, j) different from thatapplied to AC components may be employed as described below.

For example, in the case in which the Hadamard transform is employed, a4×4-size Hadamard transform is represented by equation (35).

$\begin{matrix}\begin{pmatrix}1 & 1 & 1 & 1 \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1 \\1 & 1 & 1 & {- 1}\end{pmatrix} & (35)\end{matrix}$

W(i, j) used in quantization after completion of the Hadamard transformis defined in a similar manner to W(i, j) described above. Morespecifically, W(i, j) given by equation (36) may be employed.

$\begin{matrix}{{W_{{luma}\;\_\;{dc}}\left( {i,j} \right)} = \begin{pmatrix}0 & 1 & 2 & 3 \\1 & 2 & 3 & 4 \\2 & 3 & 4 & 5 \\3 & 4 & 5 & 6\end{pmatrix}} & (36)\end{matrix}$

Using W(i, j) given by equation (36), QQP(i, j) can be determinedaccording to equation (37), and respective frequency components arequantized with the quantization step sizes corresponding to QQP(i, j).QQP(i,j)=QP+W _(luma) _(—) _(dc)(i,j)  (37)

On the other hand, a 2×2-size Hadamard transform is given by equation(38).

$\begin{matrix}\begin{pmatrix}1 & 1 \\1 & {- 1}\end{pmatrix} & (38)\end{matrix}$

W(i, j) to be used in the quantization of the coefficients having beensubjected to the Hadamard transform is obtained by simply modifying W(i,j) employed in the previous embodiment into a 2×2 size. The quantizationscale applied to each frequency component is given by adding the matrixcomponent to the quantization scale QP. W(i, j) applied to DC componentsof the color difference signal may be given, for example, by equation(39).

$\begin{matrix}{{W_{{chroma}\;\_\;{dc}}\left( {i,j} \right)} = \begin{pmatrix}0 & 1 \\1 & 2\end{pmatrix}} & (39)\end{matrix}$

Using W(i, j) given by equation (39), QQP(i, j) can be determinedaccording to equation (40), and respective frequency components arequantized with the quantization step sizes corresponding to QQP(i, j).QQP(i,j)=QP+W _(chroma) _(—) _(dc)(i,j)  (40)

As described above, the weighting matrix W(i, j) different from thatapplied to the AC components is applied to the DC components so as toimprove the accuracy of the DC components which are important to obtainhigh image quality, while reducing the amount of information associatedwith AC components to achieve high coding efficiency.

FIGS. 8 and 9 show examples of syntax for embedding informationassociated with the weighting matrix applied to the DC components intocompressed image information.

The syntax shown in FIG. 8 includes, in addition to the syntax shown inFIG. 6, 1-bit flags load_luma_dc_matrix and load_chroma_dc_matrixnecessary to embed information associated with the weighting matrixapplied to the DC components into compressed image information. Thoseflags indicate whether W(i, j) should be changed for a present picture,GOP, or sequence. If the flags have a value of 0, the current values ordefault values are used for W(i, j). If the flags have a value of 1, thevalues of respective components of 4×4 matrix W(i, j) and 2×2 matrixW(i, j) are transmitted.

The values of respective components are not necessarily needed to becoded in 4 bits, but they may be coded by means of UVLC (UniversalVariable Length Coding) employed in the H.26L standard, as shown in FIG.9, or differences from previous component values may be coded by meansof DPCM or the like.

Information associated with the weighting matrix W(i, j) may betransmitted on a GOP-by-GOP basis. In this case, syntax shown in FIG. 10may be employed.

Instead of using 1-bit flags such as load_xxx_matrix, W(i, j) isdirectly transmitted when a change is needed, as shown in FIG. 11. Inthis case, the respective components may be coded by means of UVLC asshown in FIG. 12.

Referring now to FIG. 13, an image information coding and transmittingsystem according to the first embodiment of the present invention isdescribed below.

In H.26L (JVT codec), an image signal coder (Video Coding Layer (VCL))for coding an image signal and a multiplex packetizer (Network AdaptionLayer (NAL)) for transmitting the coded image signal in a specified fileformat over a network are separately constructed in an image informationcoding and transmitting system. FIG. 13 shows an example of aconstruction of such an image information coding and transmittingsystem.

In the image information coding and transmitting system 50 shown in FIG.13, an image signal coder 51 performs coding on an image signal inaccordance with one of the embodiments described above. The compressedimage information output from the image signal coder 51 includesseparate elements corresponding to respective syntaxes.

The compressed image information (syntax elements) 62, boundaryinformation 63 indicating the boundaries of syntax elements, and headerinformation 61 including flags (corresponding to a sequence header, aGOP header, and a start code in the MPEG2) necessary to decode therespective syntax elements are supplied from the image signal coder 51to the multiplex packetizer 52.

In a case in which the compressed image information 62 is transmitted inaccordance with RTP (Real-time Transfer Protocol) (via an IP network54), the multiplex packetizer 52 maps the respective syntax elements 62onto RTP packets 65 in accordance with a predetermined method. A headernecessary in decoding is also mapped.

The header may be transmitted in a different packet (a header packet 66in the example shown in FIG. 13). Because the header includes importantinformation necessary in decoding, the header may be transmitted via adifferent channel to minimize occurrence of errors.

In this case, to transmit the weighting matrix W(i, j), the multiplexpacketizer 52 maps it together with the header information 61 necessaryin decoding into an RPT packet 65 according to a predetermined method.For this purpose, syntax shown in FIG. 14 or 15 may be employed.

The multiplex packetizer 52 may transmit the compressed imageinformation 62 via an MPEG system 53. In this case, the multiplexpacketizer 52 multiplexes the respective syntax elements 62 of thecompressed image information and the associated header information 61necessary in decoding into an MPEG system stream 64 and transmits theresultant MPEG system stream 64. In this case, the multiplex packetizer52 adds a start code at the beginning of each access unit and also addsa sequence header, a GOP header, and user data at the beginning ofparticular access units.

In this case, when the weighting matrix W(i, j) is transmitted, it isadded at the beginning of each access unit together with the headerinformation.

In MPEG, the access unit is a picture. In H.26L, in contrast, the accessunit is a slice. That is, in the case of H.26L, the weighting matrixW(i, j) is added at the beginning of each slice.

After adding the above information to the compressed image information,the multiplex packetizer 52 packetizes the data of respective accessunits into the MPEG system stream 64 and transmits the resultant MPEGsystem stream 64.

The technique described above may be applied to other transmissionschemes other than MPEG, such as RTP.

Third Modification

In the second modification described above, the first orthogonaltransform and quantization are performed on an input image signal, andthe 4×4 and 2×2 second orthogonal transform and quantization areperformed on 16 DC components of the luminance signal of a macroblock tobe intra-coded and 4 DC components of the color difference signal to beintra-coded. In the quantization, the weighting factors for respectivefrequency components are given by the weighting matrix W(i, j).

Alternatively, in the quantization performed after the first or secondorthogonal transform, the respective frequency components may be equallyweighted, as described below.

That is, the quantization after the first orthogonal transform isperformed using the quantization scale QP included in the compressedimage information to be transmitted, in accordance with, for example,equation (8).

On the other hand, in the quantization after the second orthogonaltransform, the QP in equation (8) is replaced with QQP calculatedaccording to equation (41).QQP=QP+X  (41)

In equation (41), a parameter X is an integer, and thus the respectivefrequency components are equally weighted. The weighting on QP isperformed by the weighter 16 in the image information coding apparatus10 (FIG. 2) described earlier.

Similarly, the dequantization is performed by the weighter 34 of theimage information decoding apparatus (FIG. 3) using QP or QQP inaccordance with equation (9).

The parameter X may be transmitted together with the compressed imageinformation from the coding apparatus to the decoding apparatus, whichmay extract the parameter X from the received compressed imageinformation and may use it in the second dequantization.

For example, when the parameter X used in the second quantization istransmitted on the GOP-by-GOP or picture-by-picture basis, the syntaxshown in FIG. 14 or FIG. 15 may be employed. In FIGS. 14 and 15, theparameter X is represented by DC_quant_weight.

Although flags have a fixed length of 4 bits in the examples shown inFIGS. 14 and 15, the length may be set arbitrarily. The flags may becoded by means of UVLC and the coded flags may be transmitted.

The multiplex packetizer 52 shown in FIG. 13 may multiplex and transmitthe parameter X separately from the compressed image informationgenerated by the image signal coder 51.

As described above in detail, in the image information codingmethod/apparatus according to the first embodiment of the presentinvention, an input image signal is divided into blocks, an orthogonaltransform is performed on the blocks on a block-by-block basis, andresultant orthogonal transform coefficients are quantized, wherein, inthe quantization, weighting is performed for each component of theorthogonal transform coefficients by means of an addition operation on aparameter QP specifying one of elements of a series of numbers arrangedin accordance with a predetermined rule in correspondence withquantization step sizes.

In this image information coding method/apparatus, an array A(QP)consisting of elements having values which increase or decrease by α%with increasing of the value of the parameter QP by 1 is used as thesequence of numbers corresponding to the quantization step sizes, andthe quantization is performed such that the orthogonal transformcoefficients K are multiplied by the values of the array A(QP) and theresultant product is quantized.

Furthermore, in this image information coding method/apparatus, when theparameter QP exceeds an upper limit or a lower limit, the array A(QP) isextended so as to have an extended value or values determined on thebasis of the increasing or decreasing ratio of the original array A(QP),and the extended value or values of the A(QP) are used for the exceedingvalue or values of the parameter QP.

That is, in this image information coding method/apparatus, thequantization is performed such that the orthogonal transform coefficientis first multiplied by the value of the array A(QP) and then theresultant product is quantized, wherein QP is a parameter specifying oneof elements of a series of numbers arranged in accordance with apredetermined rule in correspondence with quantization step sizes andthe value of the array A(QP) increases or decreases by α% withincreasing of the value of the parameter QP by 1.

When the parameter QP exceeds an upper limit or a lower limit, the arrayA(QP) may be extended so as to have an extended value or valuesdetermined on the basis of the increasing or decreasing ratio of theoriginal array A(QP), and the extended value or values of the A(QP) maybe used for the exceeding value or values of the parameter QP.

Thus, it becomes possible to use greater quantization step sizes inquantizing orthogonal transform coefficients in the high frequency rangein which the great quantization step sizes does not result insignificant visually-perceptible degradation, than in the low frequencyrange in which degradation is easily perceptible.

Furthermore, it becomes possible to prevent a spurious contour line frombeing created in an image including a part with gradually varying pixelvalues and it also becomes possible to perform high-efficientcompression at low bit rates.

In the image information coding method/apparatus according to the firstembodiment of the invention, an input image information may be coded bydividing the input image signal into first blocks, performing a firstorthogonal transform on the first blocks on a block-by-block basis,forming second blocks including only DC components of orthogonaltransform coefficients obtained via the first orthogonal transform, andperforming a second orthogonal transform on the second blocks; andquantizing the coefficients of AC components obtained via the firstorthogonal transform and quantizing the coefficients of the DC componentobtained via the second orthogonal transform, wherein, in thequantization, coefficients of the AC components obtained via the firstorthogonal transform may be weighted differently from the coefficientsof the DC components obtained via the second orthogonal transform.

That is, in this image information coding method/apparatus, coefficientsof DC components obtained via the first orthogonal transform areextracted, and the second orthogonal transform is performed on theextracted coefficients, and the coefficients of AC components obtainedvia the first orthogonal transform and the coefficients of DC componentsobtained via the second orthogonal transform are quantized in weightedfashion such that the coefficients of AC components are weighteddifferently from the coefficients of DC components.

This allows improvement in accuracy of the DC components which areimportant to obtain high image quality, while allowing reduction in theamount of information associated with AC components, thereby achievinghigh coding efficiency.

In the image information decoding method/apparatus according to thefirst embodiment, when compressed image information is given which hasbeen coded via a process including the steps of dividing an input imagesignal into blocks, performing an orthogonal transform on the blocks ona block-by-block basis, and quantizing resultant orthogonal transformcoefficients, the given image information is decoded by performingdequantization and an inverse orthogonal transform, wherein, in thedequantization, weighted dequantization is performed on each componentof the quantized coefficients by means of an addition operation on aparameter QP specifying one of elements of a series of numbers arrangedin accordance with a predetermined rule in correspondence withquantization step sizes.

In this image information decoding method/apparatus, an array B(QP)consisting of elements having values which increase or decrease by β%with increasing of the value of the parameter QP by 1 is used as thesequence of numbers corresponding to the quantization step sizes, andthe dequantization is performed by multiplying the quantizedcoefficients by the values of the array B(QP).

In this image information decoding method/apparatus, when the parameterQP exceeds an upper limit or a lower limit, the array B(QP) is extendedso as to have an extended value or values determined on the basis of theincreasing or decreasing ratio of the original array B(QP), and theextended value or values of the B(QP) are used for the exceeding valueor values of the parameter QP.

That is, in this image information decoding method/apparatus, thedequantization is performed such that the quantized coefficient ismultiplied by the value of the array B(QP), wherein QP is a parameterspecifying one of elements of a series of numbers arranged in accordancewith a predetermined rule in correspondence with quantization stepsizes, and the value of the array B(QP) increases or decreases by β%with increasing of the value of the parameter QP by 1.

When the parameter QP exceeds an upper limit or a lower limit, the arrayB(QP) is extended so as to have an extended value or values determinedon the basis of the increasing or decreasing ratio of the original arrayB(QP), and the extended value or values of the B(QP) are used for theexceeding value or values of the parameter QP.

Thus, in decoding of compressed image information, it becomes possibleto use greater quantization step sizes in dequantizing orthogonaltransform coefficients in the high frequency range in which the greatquantization step sizes does not result in significantvisually-perceptible degradation, than in the low frequency range inwhich degradation is easily perceptible.

In the image information decoding method/apparatus according to thefirst embodiment of the present invention, when image information isgiven which has been coded via a process including the steps of fordecoding an input image signal which has been decoded via a processincluding the steps of dividing an input image signal into first blocks,performing a first orthogonal transform on the first blocks on ablock-by-block basis, forming second blocks including only DC componentsof orthogonal transform coefficients obtained via the first orthogonaltransform, and performing a second orthogonal transform on the secondblocks; and quantizing the coefficients of AC components obtained viathe first orthogonal transform and the coefficients of DC componentsobtained via the second orthogonal transform such that the coefficientsof the AC components obtained via the first orthogonal transform wereweighted differently from the coefficients of the DC components obtainedvia the second orthogonal transform, the given image information isdecoded via a process including the steps of dequantizing the quantizedcoefficients of AC components and the coefficients of DC componentsquantized after completion of the second orthogonal transform such thatthe quantized coefficients of AC components and the coefficients of DCcomponents are weighted differently by amounts corresponding to theweights employed in the quantization.

That is, in this image information decoding method/apparatus, whencompressed image information is given which has been quantized such thatcoefficients of DC components obtained via the first orthogonaltransform were extracted, and the second orthogonal transform wasperformed on the extracted coefficients, and the coefficients of ACcomponents obtained via the first orthogonal transform and thecoefficients of DC components obtained via the second orthogonaltransform were quantized in weighted fashion such that the coefficientsof AC components were weighted differently from the coefficients of DCcomponents, the dequantization of the given image information isperformed such that the quantized coefficients of AC components and thecoefficients of DC components quantized after being subjected to thesecond orthogonal transform are respectively dequantized with differentweights corresponding to the weights employed in the quantization.

This allows improvement in accuracy of the DC components which areimportant to obtain high image quality, while allowing reduction in theamount of information associated with AC components, thereby achievinghigh coding efficiency.

In the image information coding and decoding method according to thefirst embodiment of the present invention, an input image signal iscoded by dividing the input image signal into blocks, performing anorthogonal transform on the blocks on a block-by-block basis, andquantizing resultant orthogonal transform coefficients, and theresultant compressed image signal is decoded,

wherein the quantization process includes the steps of:

preparing two arrays A(QP) and B(QP) which satisfy the followingrelationship for a parameter (0 {<=} QP {<=} n−1, where n is an integer)specifying one of elements of a series of numbers arranged in accordancewith a predetermined rule in correspondence with quantization step sizesA(QP)×B(QP)=Const, where Const denotes a constant,

and performing quantization in accordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

the dequantization is performed in accordance with the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient,

wherein normalization in the orthogonal transform is performed at thesame time for the quantization and the dequantization, and whereinweighted quantization and weighted dequantization are performed suchthat a parameter QQP(i, j) is calculated for each component of theorthogonal transform coefficients, using an array W(i, j) prepared inadvance, according to the formula QQP(i, j)=QP+W(i, j), and weightedquantization and weighted dequantization are performed using twovariables A(QQP(i, j)) and B(QQP(i, j)), respectively, which are givenby the parameter QQP(i, j) for each component.

In this image information coding and decoding method, when quantizationand dequantization are performed on the basis of the arrays A(QP) andB(QP), the parameter QQP(i, j) is calculated for each component of theorthogonal transform coefficients using the prepared array W(i, j)according to the formula QQP(i, j)=QP+W(i, j), and weighted quantizationand weighted dequantization are performed using two variables A(QQP(i,j)) and B(QQP(i, j)), respectively, which are given by the parameterQQP(i, j) for each component.

If the value of QQP(i, j) exceeds a predetermined domain, arrays A(QQP)and B(QQP) obtained by extending the dynamic ranges of the arrays A(QP)and B(QP) are used.

Thus, it becomes possible to use greater quantization step sizes inquantizing orthogonal transform coefficients in the high frequency rangein which the great quantization step sizes does not result insignificant visually-perceptible degradation, than in the low frequencyrange in which degradation is easily perceptible.

Furthermore, it becomes possible to prevent a spurious contour line frombeing created in an image including a part with gradually varying pixelvalues and it also becomes possible to perform high-efficientcompression at low bit rates.

The image information coding and transmitting system according to thefirst embodiment of the present invention includes an image signal coderfor producing compressed image information by dividing an input imagesignal into blocks, performing an orthogonal transform on the blocks ona block-by-block basis, and quantizing resultant orthogonal transformcoefficient and also producing header information; and a multiplexpacketizer for, when the compressed image information and the headerinformation are received from the image signal coder, multiplexing thecompressed image information and the header information in accordancewith a predetermined method and transmitting the resultant multiplexedinformation in the form of packets, wherein when the image signal coderquantizes orthogonal transform coefficients obtained via the orthogonaltransform, the image signal coder performs weighted quantization on eachcomponent of the orthogonal transform coefficients by means of anaddition operation on a parameter QP specifying one of elements of aseries of numbers arranged in accordance with a predetermined rule incorrespondence with quantization step sizes; and the multiplexpacketizer multiplexes information associated with the quantizationweighting together with the header information and packetizes themultiplexed information.

The image information coding and transmitting system according to thefirst embodiment of the present invention may include an image signalcoder for producing compressed image information by dividing an inputimage signal into blocks, performing an orthogonal transform on theblocks on a block-by-block basis, and quantizing resultant orthogonaltransform coefficient and also producing header information; and amultiplex packetizer for, when the compressed image information and theheader information are received from the image signal coder,multiplexing the compressed image information and the header informationin accordance with a predetermined method and transmitting the resultantmultiplexed information in the form of packets, wherein the multiplexpacketizer adds at least the header information to each access unit, atthe beginning thereof, of the compressed image information.

The image information coding and transmitting system according to thefirst embodiment of the present invention may include an image signalcoder for producing compressed image information by dividing an inputimage signal into blocks, performing an orthogonal transform on theblocks on a block-by-block basis, and quantizing resultant orthogonaltransform coefficient and also producing header information; and amultiplex packetizer for, when the compressed image information and theheader information are received from the image signal coder,multiplexing the compressed image information and the header informationin accordance with a predetermined method and transmitting the resultantmultiplexed information in the form of packets, wherein when the imagesignal coder quantizes orthogonal transform coefficients obtained viathe orthogonal transform, the image signal coder performs weightedquantization on each component of the orthogonal transform coefficientsby means of an addition operation on a parameter QP specifying one ofelements of a series of numbers arranged in accordance with apredetermined rule in correspondence with quantization step sizes; andthe multiplex packetizer multiplexes information associated with thequantization weighting together with the header information, packetizingthe resultant multiplexed information separately from the compressedimage information, and transmits the resultant packetized informationand the compressed image information separately via different channels.

Second Embodiment

In the first embodiment described above, quantization and dequantizationare performed using the quantization parameter QP_(luma) as thequantization parameter Q for the luminance signal.

However, when the quantization parameter QP_(luma) is increased by 1,the quantization parameter QP_(chroma) applied to the color differencesignal does not necessarily increase by 1. Thus, in the imageinformation coding apparatus (for example, the image information codingapparatus 10 shown in FIG. 1) and in the image information decodingapparatus (for example, the image information decoding apparatus 30shown in FIG. 2) according to the first embodiment, simple weighting onthe luminance signal according to equation (10) does not necessarilycause the color difference signal to be properly weighted.

The image information coding apparatus and the image informationdecoding apparatus according to the second embodiment described hereinare based on the first embodiment, but improvements are made so as tosolve the above-described problem. That is, in the image informationcoding apparatus and the image information decoding apparatus accordingto the second embodiment, weighting on the color difference signal ispossible even in the case in which the quantization parameter QP_(luma)applied to the luminance signal and the quantization parameterQP_(chroma) applied to the color difference signal can have differentvalues as with the process according to the H.26L standard, and thosevalues are represented by a single parameter QP described in compressedimage information.

FIG. 16 shows an example of a construction of an image informationcoding apparatus 71 according to the second embodiment of the presentinvention, in which similar parts to those of the image informationcoding apparatus 10 shown in FIG. 1 are denoted by similar referencenumerals.

In this construction, the quantizer 15 shown in FIG. 1 is replaced witha quantizer 81, and the dequantizer 19 shown in FIG. 1 is replaced withan dequantizer 82.

The other parts are similar to those of the image information codingapparatus 10 shown in FIG. 1.

In contrast to the quantizer 15 having a single weighter 16 shown inFIG. 1, the quantizer 81 includes two weighters, that is, a luminancesignal weighter 91 for performing weighting on the luminance signal anda color difference signal weighter 92 for performing weighting on thecolor difference signal.

Similarly, in contrast to the dequantizer having a single weighter 20shown in FIG. 1, the dequantizer 82 includes two weighters, that is, aluminance signal weighter 93 for performing weighting on the luminancesignal and a color difference signal weighter 94 for performingweighting on the color difference signal.

FIG. 17 shows an example of a construction of an image informationdecoding apparatus 101 according to the second embodiment of the presentinvention, in which similar parts to those of the image informationdecoding apparatus 30 shown in FIG. 2 are denoted by similar referencenumerals.

In this construction, the dequantizer 33 shown in FIG. 2 is replacedwith a dequantizer 111.

The other parts are similar to those of the image information decodingapparatus 30 shown in FIG. 2.

In contrast to the dequantizer 33 having a single weighter 34 shown inFIG. 2, the dequantizer 111 includes two weighters, that is, a luminancesignal weighter 121 and a color difference signal weighter 122.

The operation of the image information coding apparatus 71 (FIG. 16) isbasically similar to that of the image information coding apparatus 10(FIG. 1) except for the operation of the color difference signalweighter 92 in the quantizer 81 and the operation of the colordifference signal weighter 94 in the dequantizer 82.

The operation of the image information decoding apparatus 101 (FIG. 17)is basically similar to that of the image information decoding apparatus30 (FIG. 2) except for the operation of the color difference signalweighter 122 in the quantizer 111.

The operation of the luminance signal weighter 91 in the quantizer 81(FIG. 16), the operation of the luminance signal weighter 93 in thedequantizer 82 (FIG. 16), and the operation of the luminance signalweighter 121 in the dequantizer 111 (FIG. 17) are basically similar tothose of the weighter 16 in the quantizer 15 (FIG. 1), the weighter 20in the dequantizer 19 (FIG. 1), and the weighter 34 in the dequantizer33 (FIG. 2), respectively.

That is, the luminance signal weighter 91 in the quantizer 81 (FIG. 16),the luminance signal weighter 93 in the dequantizer 82 (FIG. 16), andthe luminance signal weighter 121 in the dequantizer 111 (FIG. 17)perform weighting on the luminance signal in accordance with equation(10).

However, for the purpose of distinction from equation (46) (applied tothe weighting on the color difference signal), equation (10) isrewritten as equation (42).QQP _(luma)(i,j)=QP _(luma)(QP)+W(i,j)  (42)

The operation of the color difference signal weighter 92 in thequantizer 81 (FIG. 16), the operation of the color difference signalweighter 94 in the dequantizer 82 (FIG. 16), and the operation of thecolor difference signal weighter 122 in the dequantizer 111 (FIG. 17)are basically similar to each other.

Thus, herein, only the operation of the color difference signal weighter92 in the quantizer 81 is described.

In FIG. 16, by way of example, we assume that the quantization parameterQP associated with a macroblock input to the quantizer 81 has a value of17 (QP=17), and a weighting matrix shown in FIG. 3 is applied to thatmacroblock.

In this case, calculation of equation (10) yields a value of 18 forQQP(0, 2), as can be seen from equation (43).

$\begin{matrix}\begin{matrix}{{{QQP}\left( {0,2} \right)} = {{QP} + {W\left( {0,2} \right)}}} \\{= {17 + 1}} \\{= 18}\end{matrix} & (43)\end{matrix}$

The value of the parameter QQP(0, 2) is calculated on the basis of theparameter QP_(luma) applied to the luminance signal, as described above.Thus, although the parameter QQP_(luma)(0, 2) applied to the luminancesignal becomes 18 as shown in FIG. 44), the parameter QP_(chroma)(0, 2)applied to the color difference signal does not become 18 but 17, asshown in equation (45) (because of the relationship between theparameter QQP_(luma) and the parameter QQP_(chroma) as describedearlier).QQP _(luma)(0,2)=18  (44)QQP _(chroma)(0,2)=17  (45)

Therefore, the weighting process according to equation (10) cannotproperly impose weighting on the color difference signal.

To avoid the above problem, the color difference signal weighter 92performs weighting on the color difference signal in accordance withequation (46) instead of equation (10) (equation (42)).QQP _(chroma)(i,j)=QP _(chroma)(QP)+W(i,j)  (46)

More specifically, in this specific example, the color difference signalweighter 92 calculates the value of the parameter QQP_(chroma)(0, 2) asshown in equation (47).

$\begin{matrix}\begin{matrix}{{{QQP}_{chroma}\left( {0,2} \right)} = {{{QP}_{chroma}\left( {{QP} = 17} \right)} + {W\left( {0,2} \right)}}} \\{= {17 + 1}} \\{= 18}\end{matrix} & (47)\end{matrix}$

As described above, the quantizer 81 performs weighting on the luminancesignal component using the luminance signal weighter 91 and on the colordifference signal component using the color difference signal weighter92.

As described earlier, in the current H.26L standard, the upper limit ofthe parameter QQP_(chroma)(i, j) is defined to be 26. However, when theparameter QQP_(chroma)(i, j) is determined according to equation (46),the resultant value can become greater than upper limit (26).

In such a case, the color difference signal weighter 92 performsweighting according to one of two methods described below, although themethod is not limited to those.

According to a first method, when the color difference signal weighter92 calculates the value of the parameter QQP_(chroma) according toequation (46), if the resultant value exceeds the upper limit (26), thecalculated value (greater than 26) is not used but the value equal tothe upper limit (26) is employed as the value of the parameterQQP_(chroma)(i, j). That is, if the calculated value of the parameterQQP_(chroma)(i, j) is greater than 26, the color difference signalweighter 92 recalculates the value of the parameter QQP_(chroma)(i, j)according to equation (48).QQP _(chroma)(i,j)=26  (48)

According to the second method, if the calculated value of the parameterQQP_(chroma)(i, j) exceeds the upper limit (26), the arrayA(QQP_(chroma)(i, j)) and the array B(QQP_(chroma)(i, j)) are extendedin accordance with equations (49) and (50) for the calculated value ofthe parameter QQP_(chroma)(i, j).

$\begin{matrix}{{A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > 26} \right)} = {{round}\left( \frac{27}{1.12^{{{QQP}_{chroma}{({i,j})}} - 26}} \right)}} & (49) \\{{B\left( {{{QQP}_{chroma}\left( {i,j} \right)} > 26} \right)} = {{round}\left( {89113 \times 1.12^{{{QQP}_{chroma}{({i,j})}} - 26}} \right)}} & (50)\end{matrix}$where round( ) denotes a round-into-integer function.

As described above, the quantizer 81 of the <image information codingapparatus 71 (FIG. 16) uses, as the quantization parameter QP, theparameter QP_(luma) applied to the luminance signal and the parameterQP_(chroma) applied to the color difference signal, and the quantizer 81includes the luminance signal weighter 91 for calculating the parameterQQP_(luma)(i, j) by adding a weighting array W(i, j) to the array of theparameter QP_(luma) corresponding to the respective components of theluminance signal in each block (in accordance with equation (10) or(42)) and also includes the color difference signal weighter 92 forcalculating the parameter QQP_(chroma)(i, j) by adding the array W(i, j)to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal in each block (inaccordance with equation (46)), wherein the quantizer 81 performsweighted quantization using the parameter QP_(luma)(i, j) calculated bythe luminance signal weighter 91 and the parameter QQP_(chroma)(i, j)calculated by the color difference signal weighter 92.

When the parameter QQP_(chroma)(i, j) calculated by the color differencesignal weighter 92 exceeds the predetermined upper limit QQP_(chroma)_(—) _(max) (26 in the present example), the quantizer 81 performsweighted quantization in accordance with one of methods described below.

In a first method, the quantizer 81 performs weighted quantization usinga value equal to the upper limit QQP_(chroma) _(—) _(max) as theparameter QQP_(chroma)(i, j).

In the second method, in the case in which coding of an input imagesignal is performed such that two arrays A(QP) and B(QP) correspondingto the parameter QP and having the following relationship (51) arepreparedA(QP)×B(QP)=Const (where Const denotes a constant)  (51)

the quantization is performed in accordance with the following formula(52)LEVEL=(K×A(QP)+f×2^(m))/2^(m)  (52)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

dequantization corresponding to the quantization is to be performed inaccordance with the following formula (53)K′=LEVEL×B(QP)  (53)where K′ denotes a dequantized orthogonal transform coefficient,

the quantizer 81 performs quantization such that

a common ration r is calculated in accordance with the following formula(54)

$\begin{matrix}{\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}} & (54)\end{matrix}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas (55) and (56)

$\begin{matrix}{{A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{{chroma}\;\_\;\max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{{chroma}\;\_\;\max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{{chroma}\;\_\;\max}}} \right)}} & (55) \\{{B\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{{chroma}\;\_\;\max}} \right)} = {{round}\left( {{A\left( {QQP}_{{chroma}\;\_\;\max} \right)} \times r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{{chroma}\;\_\;\max}}} \right)}} & (56)\end{matrix}$where round( ) denotes a round-into-integer function, and

the quantization is performed in accordance with the following formula(57)LEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))+f×2^(m))/2^(m)

As with the quantizer 81 (FIG. 16), the dequantizer 82 (FIG. 16) and thedequantizer 111 (FIG. 17) also use as the quantization parameter QP, theparameter QP_(luma) applied to the luminance signal and the parameterQP_(chroma) applied to the color difference signal, and they include theluminance signal weighter 93 or 121 for calculating the parameterQQP_(luma)(i, j) by adding a weighting array W(i, j) to the array of theparameter QP_(luma) corresponding to the respective components of theluminance signal in each block (in accordance with equation (10) or(42)) and also include the color difference signal weighter 94 or 122for calculating the parameter QQP_(chroma)(i, j) by adding the arrayW(i, j) to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal in each block (inaccordance with equation (46)), wherein the dequantizers 82 and 111perform weighted dequantization using the parameter QQP_(luma)(i, j)calculated by the luminance signal weighter 93 or 121 and the parameterQQP_(chroma)(i, j) calculated by the color difference signal weighter 94or 122.

When the parameter QQP_(chroma) _(—) _(max)(i, j) calculated by thecolor difference signal weighter 94 or 122 exceeds the predeterminedupper limit QQP_(chroma) _(—max) (26 in the present example), thedequantizer 82 or 111 performs weighted dequantization in accordancewith one of methods described above.

Thus, in the image information coding apparatus 71 and the imageinformation decoding apparatus 101, weighting on the color differencesignal is possible even in the case in which the quantization parameterQP_(luma) applied to the luminance signal and the quantization parameterQP_(chroma) applied to the color difference signal can have differentvalues as with the process according to the H.26L standard, and thosevalues are represented by a single parameter QP described in compressedimage information.

The technique disclosed in the second embodiment may be applied not onlyto the image information coding apparatus 71 and the image informationdecoding apparatus 101 but also to apparatuses according to the firstembodiment described earlier.

For example, the technique may be applied to the image informationcoding apparatus according to the first modification of the firstembodiment so as to include a quantizer for quantizing an input imagesignal by dividing the input image signal into first blocks, performinga first orthogonal transform on the first blocks on a block-by-blockbasis, forming second blocks including only DC components of orthogonaltransform coefficients obtained via the first orthogonal transform, andperforming a second orthogonal transform on the second blocks; andquantizing the coefficients of AC components obtained via the firstorthogonal transform and quantizing the coefficients of the DC componentobtained via the second orthogonal transform, wherein, in thequantization, coefficients of the AC components obtained via the firstorthogonal transform are weighted differently from the coefficients ofthe DC components obtained via the second orthogonal transform.

That is, in this image information coding apparatus based on the firstembodiment, in the quantization performed on the coefficients of ACcomponents obtained via the first orthogonal transform, the quantizationis performed using a parameter QP specifying one of elements of a seriesof numbers arranged according to a predetermined rule in correspondencewith quantization step sizes, and in the quantization performed on thecoefficients of DC components obtained via the second orthogonaltransform, weighted quantization is performed using a parameter QQPobtained by adding a predetermined parameter X to the parameter QP.

Furthermore, the technique disclosed in the second embodiment may beapplied to the image information coding apparatus according to the firstembodiment as described below.

A quantizer (not shown but having a similar structure to that of thequantizer 81 shown in FIG. 16) performs quantization of the coefficientsof AC components using, as the parameter QP, a parameter QP_(luma) for aluminance signal and a parameter QP_(chroma) for a color differencesignal. The quantizer includes a luminance signal weighter (not shownbut having a similar structure to the luminance signal weighter 91 shownin FIG. 16) for calculating, as the parameter QQP, the parameterQQP_(luma)(i, j) by adding a weighting array W(i, j) as the parameter Xto the array of the parameter QP_(luma) corresponding to the respectivecomponents of the luminance signal in each block, and the quantizer alsoincludes a color difference signal weighter (not shown but having asimilar structure to the color difference signal weighter 92 shown inFIG. 16) for calculating, as the parameter QQP, the parameterQQP_(chroma)(i, j) by adding the weighting array W(i, j) as theparameter X to the array of the parameter QP_(chroma) corresponding tothe respective components of the color difference signal in each block.The quantizer performs weighted quantization of the coefficients of DCcomponents, using the parameter QQP_(luma)(i, j) calculated by theluminance signal weighter and the parameter QQP_(chroma)(i, j)calculated by the color difference signal weighter.

When the parameter QQP_(chroma)(i, j) calculated by the color differencesignal weighter exceeds the predetermined upper limit QQP_(chroma) _(—)_(max) (26 in the present example), the quantizer performs weightedquantization of DC components in accordance with one of methodsdescribed above.

Similarly, an image information decoding apparatus (not shown)corresponding to the above-described image information coding apparatusmay be constructed as follows.

A dequantizer (not shown but having a similar structure to thedequantizer 111 shown in FIG. 17) performs dequantization of thecoefficients of AC components using, as the parameter QP, a parameterQP_(luma) for the luminance signal and a parameter QP_(chroma) for thecolor difference signal. The dequantizer includes a luminance signalweighter (not shown but having a similar structure to the luminancesignal weighter 121 shown in FIG. 17) for calculating, as the parameterQQP, the parameter QQP_(luma)(i, j) by adding a weighting array W(i, j)as the parameter X to the array of the parameter QP_(luma) correspondingto the respective components of the luminance signal in each block, andthe dequantizer also includes a color difference signal weighter (notshown but having a similar structure to the color difference signalweighter 122 shown in FIG. 17) for calculating, as the parameter QQ, theparameter QQP_(chroma)(i, j) by adding the weighting array W(i, j) asthe parameter X to the array of the parameter QP_(chroma) correspondingto the respective components of the color difference signal in eachblock. The dequantizer performs weighted dequantization of thecoefficients of DC component, using the parameter QP_(luma)(i, j)calculated by the luminance signal weighter and the parameterQQP_(chroma)(i, j) calculated by the color difference signal weighter.

When the parameter QQP_(chroma)(i, j) calculated by the color differencesignal weighter exceeds the predetermined upper limit QQP_(chroma) _(—)_(max) (26 in the present example), the dequantizer performs weighteddequantization of DC components in accordance with one of methodsdescribed above.

An image information coding and transmitting system according to thesecond embodiment corresponding to the image information coding andtransmitting system 51 according to the first embodiment shown in FIG.13 may be realized by replacing the image signal coder 51 shown in FIG.13 with an image signal coder 71 shown in FIG. 16.

The above-described process according to the first or second embodimentmay be performed by hardware or software.

In the case in which the process is performed by software, the imageinformation coding apparatus or the image information decoding apparatusmay be realized, for example, by a personal computer such as that shownin FIG. 18.

As shown in FIG. 18, a CPU (Central Processing Unit) 151 performsvarious processes in accordance with a program stored in a ROM (ReadOnly Memory) 152 or in accordance with a program loaded into a RAM(Random Access Memory) 153 from a storage unit 158. The RAM 153 is alsoused to stored data necessary for the CPU 151 to perform the processes.

The CPU 151, the ROM 152, and the RAM 153 are connected to each othervia a bus 154. The bus 154 is also connected to an input/outputinterface 155.

The input/output interface 155 is connected to an input unit 156including a keyboard, a mouse, and/or the like, an output unit 157including a display or the like, the storage unit 158 including a harddisk or the like, and a communication unit 159 including a modem, aterminal adapter, and/or the like. The communication unit 159 allowscommunication with other information processing apparatuses via networksincluding the Internet.

The input/output interface 155 is connected to a drive 160, as required.A removable storage medium 161 such as a magnetic disk, an optical disk,a magnetooptical disk, or a semiconductor memory is mounted on the drive160 as required, and a computer program is read from the removablestorage medium 161 and installed into the storage unit 158, as required.

When the processing sequence is executed by software, a program formingthe software may be installed from a storage medium onto a computerwhich is provided as dedicated hardware or may be installed onto ageneral-purpose computer capable of performing various processes inaccordance with various programs installed thereon.

Specific examples of storage media usable for the above purpose include,as shown in FIG. 18, a removable storage medium (a package medium) 161such as a magnetic disk (such as a floppy disk), an optical disk (suchas a CD-ROM (Compact Disk-Read Only Memory) and a DVD (Digital VersatileDisk)), a magnetooptical disk (such as an MD (Mini-Disk, trademark)),and a semiconductor memory, on which a program is stored and which issupplied to a user separately from a computer. A program may also besupplied to an user by preinstalling it on a built-in ROM 152 or astorage unit 158 such as a hard disk disposed in the computer.

Some examples of programs are described below, although the programs arenot limited to those.

A first image information coding program according to the firstembodiment of the present invention is a program for causing the CPU 151shown in FIG. 18 to execute coding including the steps of dividing aninput image signal into blocks, performing an orthogonal transform onthe blocks on a block-by-block basis, and quantizing orthogonaltransform coefficients, wherein, in the quantization, weighting isperformed for each component of the orthogonal transform coefficients bymeans of an addition operation on a parameter QP specifying one ofelements of a series of numbers arranged in accordance with apredetermined rule in correspondence with quantization step sizes.

In this first image information coding program, an array A(QP)consisting of elements having values which increase or decrease by a %with increasing of the value of the parameter QP by 1 is used as thesequence of numbers corresponding to the quantization step sizes, andthe quantization is performed such that the orthogonal transformcoefficients K are multiplied by the values of the array A(QP) and theresultant product is quantized.

Furthermore, in this first image information coding program, when theparameter QP exceeds an upper limit or a lower limit, the array A(QP) isextended so as to have an extended value or values determined on thebasis of the increasing or decreasing ratio of the original array A(QP),and the extended value or values of the A(QP) are used for the exceedingvalue or values of the parameter QP.

Furthermore, in this first image information coding program, thequantization is performed such that the orthogonal transform coefficientis first multiplied by the value of the array A(QP) and then theresultant product is quantized, wherein QP is a parameter specifying oneof elements of a series of numbers arranged in accordance with apredetermined rule in correspondence with quantization step sizes andthe value of the array A(QP) increases or decreases by a % withincreasing of the value of the parameter QP by 1.

When the parameter QP exceeds an upper limit or a lower limit, the arrayA(QP) may be extended so as to have an extended value or valuesdetermined on the basis of the increasing or decreasing ratio of theoriginal array A(QP), and the extended value or values of the A(QP) maybe used for the exceeding value or values of the parameter QP.

Thus, it becomes possible to use greater quantization step sizes inquantizing orthogonal transform coefficients in the high frequency rangein which the great quantization step sizes does not result insignificant visually-perceptible degradation, than in the low frequencyrange in which degradation is easily perceptible. Furthermore, itbecomes possible to prevent a spurious contour line from being createdin an image including a part with gradually varying pixel values and italso becomes possible to perform high-efficient compression at low bitrates.

An example of a second image information coding program corresponding tothe first image information coding program according to the firstembodiment is described below.

According to this program, the parameter QP may include a parameterQP_(luma) applied to a luminance signal and a luma parameter QP_(chroma)applied to a color difference signal; and the quantization is performedby the CPU 151 shown in FIG. 18 such that a parameter QQP_(luma)(i, j)is calculated by adding a weighting array W(i, j) to the array of theparameter QP_(luma) corresponding to the respective components of theluminance signal of each block, a parameter QQP_(chroma)(i, j) iscalculated by adding the weighting array W(i, j) to the array of theparameter QP_(chroma) corresponding to the respective components of thecolor difference signal of each block, and weighted dequantization isperformed using the resultant parameter QQP_(luma)(i, j) and theresultant parameter QQP_(chroma)(i, j).

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QP_(chroma) _(—) _(max), the CPU 151shown in FIG. 18 performs one of two processes corresponding to theabove-described two methods.

That is, the CPU 151 shown in FIG. 18 performs weighted quantizationusing the predetermined value QQP_(chroma) _(—) _(max) as the parameterQQP_(chroma)(i, j) or performs a process such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship are preparedA(QP)×B(QP)=Const, where Const denotes a constant,

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

dequantization corresponding to the quantization is to be performed inaccordance with the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient,

a common ration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{{chroma}\;\_\;\max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{{chroma}\;\_\;\max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{{chroma}\;\_\;\max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma _ max )) = round(A(QQP_(chroma _ max )) × r^(QQP_(chroma)(i, j) − QQP_(chroma _ max )))where round( ) denotes a round-into-integer function, and

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))+f×2^(m))/2^(m).

This makes it possible to perform weighting on the color differencesignal in a case in which the quantization parameter QP_(luma) appliedto the luminance signal and the quantization parameter QP_(chroma)applied to the color difference signal can have different values as withthe process according to the H.26L standard, and those values arerepresented by a single parameter QP in compressed image information.

A second image information coding program according to the firstembodiment of the present invention is a program for causing a computerto execute a process including the steps of dividing an input imagesignal into first blocks, performing a first orthogonal transform on thefirst blocks on a block-by-block basis, forming second blocks includingonly DC components of orthogonal transform coefficients obtained via thefirst orthogonal transform, and performing a second orthogonal transformon the second blocks; and quantizing the coefficients of AC componentsobtained via the first orthogonal transform and quantizing thecoefficients of the DC component obtained via the second orthogonaltransform, wherein, in the quantization, coefficients of the ACcomponents obtained via the first orthogonal transform are weighteddifferently from the coefficients of the DC components obtained via thesecond orthogonal transform.

In this second image information coding program, coefficients of DCcomponents obtained via the first orthogonal transform are extracted,and the second orthogonal transform is performed on the extractedcoefficients, and the coefficients of AC components obtained via thefirst orthogonal transform and the coefficients of DC componentsobtained via the second orthogonal transform are quantized in weightedfashion such that the coefficients of AC components are weighteddifferently from the coefficients of DC components.

This allows improvement in accuracy of the DC components which areimportant to obtain high image quality, while allowing reduction in theamount of information associated with AC components, thereby achievinghigh coding efficiency.

An example of a second image information coding program corresponding tothe second image information coding program according to the firstembodiment is described below.

That is, according to the program, the CPU 151 shown in FIG. 18 executesquantization of the coefficients of AC components, as the parameter QP,a parameter QP_(luma) for a luminance signal and a parameter QP_(chroma)for a color difference signal, and executes quantization of thecoefficients of DC components using, as the parameter QQP, a parameterQQP_(luma)(i, j) for the luminance signal and a parameterQQP_(chroma)(i, j) for the color difference signal, wherein theparameter QQP_(luma)(i, j) is calculated by adding a weighting arrayW(i, j) to the array of the parameter QP_(luma) corresponding to therespective components of the luminance signal of each block, and theparameter QQP_(chroma)(i, j) is calculated by adding the weighting arrayW(i, j) to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal of each block.

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max) the CPU 151shown in FIG. 18 performs one of two processes corresponding to theabove-described two methods.

That is, the CPU 151 shown in FIG. 18 performs quantization on DCcomponents using the predetermined value QQP_(chroma) _(—) _(max) as theparameter QP_(chroma)(i, j) or performs a process such that

two arrays A(QP) and B(QP) corresponding to the parameter QP and havingthe following relationship are preparedA(QP)×B(QP)=Const, where Const denotes a constant,

quantization of the coefficients of AC components is performed inaccordance with the following formulaLEVEL=(K×A(QP)+f×2^(m))/2^(m)where K denotes an unquantized orthogonal transform coefficient, mdenotes a predetermined integer, f denotes a rounding constant, LEVELdenotes a quantized output,

dequantization corresponding to the quantization is to be performed inaccordance with the following formulaK′=LEVEL×B(QP)where K′ denotes a dequantized orthogonal transform coefficient,

a common ration is calculated in accordance with the following formula

$\frac{A({QP})}{A\left( {{QP} + 1} \right)} = {\frac{B\left( {{QP} + 1} \right)}{B({QP})} = r}$

a variable A(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) and a variableB(QQP_(chroma)(i, j)>QQP_(chroma) _(—) _(max) are respectivelycalculated in accordance with the following formulas

${A\left( {{{QQP}_{chroma}\left( {i,j} \right)} > {QQP}_{{chroma}\;\_\;\max}} \right)} = {{round}\left( \frac{A\left( {QQP}_{{chroma}\;\_\;\max} \right)}{r^{{{QQP}_{chroma}{({i,j})}} - {QQP}_{{chroma}\;\_\;\max}}} \right)}$B(QQP_(chroma)(i, j) > QQP_(chroma _ max )) = round(A(QQP_(chroma _ max )) × r^(QQP_(chroma)(i, j) − QQP_(chroma _ max )))where round( ) denotes a round-into-integer function, and

the quantization is performed in accordance with the following formulaLEVEL=(K×A(QQP _(chroma)(i,j)>QQP _(chroma) _(—) _(max))+f×2^(m))/2^(m).

This makes it possible to perform weighting on the color differencesignal in a case in which the quantization parameter QP_(luma) appliedto the luminance signal and the quantization parameter QP_(chroma)applied to the color difference signal can have different values as withthe process according to the H.26L standard, and those values arerepresented by a single parameter QP in compressed image information.

A first image information decoding program according to the firstembodiment of the present invention causes the CPU 151 shown in FIG. 18to execute a process of decoding compressed image information which hasbeen coded via a process including the steps of dividing an input imagesignal into blocks, performing an orthogonal transform on the blocks ona block-by-block basis, and quantizing resultant orthogonal transformcoefficients, wherein, in the dequantization, weighted dequantization isperformed on each component of the quantized coefficients by means of anaddition operation on a parameter QP specifying one of elements of aseries of numbers arranged in accordance with a predetermined rule incorrespondence with quantization step sizes.

In the first image information decoding program, an array B(QP)consisting of elements having values which increase or decrease by β%with increasing of the value of the parameter QP by 1 may be used as thesequence of numbers corresponding to the quantization step sizes, andthe dequantization is performed by multiplying the quantizedcoefficients by the values of the array B(QP).

In this first image information decoding program, when the parameter QPexceeds an upper limit or a lower limit, the array B(QP) is extended soas to have an extended value or values determined on the basis of theincreasing or decreasing ratio of the original array B(QP), and theextended value or values of the B(QP) are used for the exceeding valueor values of the parameter QP.

That is, in the first image information decoding program, thedequantization is performed such that the quantized coefficient ismultiplied by the value of the array B(QP), wherein QP is a parameterspecifying one of elements of a series of numbers arranged in accordancewith a predetermined rule in correspondence with quantization stepsizes, and the value of the array B(QP) increases or decreases by β%with increasing of the value of the parameter QP by 1.

When the parameter QP exceeds an upper limit or a lower limit, the arrayB(QP) may be extended so as to have an extended value or valuesdetermined on the basis of the increasing or decreasing ratio of theoriginal array B(QP), and the extended value or values of the B(QP) maybe used for the exceeding value or values of the parameter QP.

Thus, in decoding of compressed image information, it becomes possibleto use greater quantization step sizes in dequantizing orthogonaltransform coefficients in the high frequency range in which the greatquantization step sizes does not result in significantvisually-perceptible degradation, than in the low frequency range inwhich degradation is easily perceptible.

An example of a second image information decoding program correspondingto the first image information decoding program according to the firstembodiment is described below.

That is, in this program, the parameter QP may include a parameterQP_(chroma) applied to a luminance signal and a parameter QP_(chroma)applied to a color difference signal; and the dequantization isperformed by the CPU 151 shown in FIG. 18 such that a parameterQQP_(luma)(i, j) is calculated by adding a weighting array W(i, j) tothe array of the parameter QP_(luma) corresponding to the respectivecomponents of the luminance signal of each block, a parameterQQP_(chroma)(i, j) is calculated by adding the weighting array W(i, j)to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal of each block, andweighted dequantization is performed using the resultant parameterQQP_(luma)(i, j) and the resultant parameter QQP_(chroma)(i, j).

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max) the CPU 151shown in FIG. 18 performs one of two processes corresponding to theabove-described two methods.

The second image information decoding program according to the firstembodiment of the present invention may cause the CPU 151 shown in FIG.18 to execute a process of decoding image information which has beencoded via a process including the steps of dividing an input imagesignal into first blocks, performing a first orthogonal transform on thefirst blocks on a block-by-block basis, forming second blocks includingonly DC components of orthogonal transform coefficients obtained via thefirst orthogonal transform, and performing a second orthogonal transformon the second blocks; and quantizing the coefficients of AC componentsobtained via the first orthogonal transform and the coefficients of DCcomponents obtained via the second orthogonal transform such that thecoefficients of the AC components obtained via the first orthogonaltransform were weighted differently from the coefficients of the DCcomponents obtained via the second orthogonal transform, wherein thedecoding process includes the step of dequantizing the quantizedcoefficients of AC components and the coefficients of DC componentsquantized after completion of the second orthogonal transform such thatthe quantized coefficients of AC components and the coefficients of DCcomponents are weighted differently by amounts corresponding to theweights employed in the quantization.

In the second image information decoding program, when a compressedimage information is given which has been coded such that coefficientsof DC components obtained via the first orthogonal transform wereextracted, and the second orthogonal transform was performed on theextracted coefficients, and the coefficients of AC components obtainedvia the first orthogonal transform and the coefficients of DC componentsobtained via the second orthogonal transform were quantized in weightedfashion such that the coefficients of AC components were weighteddifferently from the coefficients of DC components, the dequantizationof the given image information is performed such that the quantizedcoefficients of AC components and the coefficients of DC componentsquantized after being subjected to the second orthogonal transform arerespectively dequantized with different weights corresponding to theweights employed in the quantization.

This allows improvement in accuracy of the DC components which areimportant to obtain high image quality, while allowing reduction in theamount of information associated with AC components.

An example of a second image information coding program corresponding tothe second image information coding program according to the firstembodiment is described below.

That is, according to the program, the CPU 151 shown in FIG. 18 executesdequantization of the coefficients of AC components using, as theparameter QP, a parameter QP_(luma) for a luminance signal and aparameter QP_(chroma) for a color difference signal, and executesquantization of the coefficients of DC components using, as theparameter QQP, a parameter QQP_(luma)(i, j) for the luminance signal anda parameter QQP_(chroma)(i, j) for the color difference signal, whereinthe parameter QP_(luma)(i, j) is calculated by adding a weighting arrayW(i, j) to the array of the parameter QP_(luma) corresponding to therespective components of the luminance signal of each block, and theparameter QQP_(chroma)(i, j) is calculated by adding the weighting arrayW(i, j) to the array of the parameter QP_(chroma) corresponding to therespective components of the color difference signal of each block.

When the parameter QQP_(chroma)(i, j) obtained via the calculationexceeds the predetermined value QQP_(chroma) _(—) _(max), the CPU 151shown in FIG. 18 performs one of two processes corresponding to theabove-described two methods.

The techniques disclosed in the present invention may be applied tovarious transform schemes. That is, the techniques may be employedregardless of the calculation accuracy or the integer transform matrix.

Furthermore, the present invention may be employed regardless of thetransform block size. The invention may also be applied to an adaptivevariable block size transform in which the frequency transform isperformed while adaptively changing the block size among 4×4, 4×8, 8×4,8×8, and 16×16.

Although the present invention has been described above with referenceto specific embodiments, the invention is not limited to thoseembodiments, but various modifications are possible without departingfrom the scope of the invention.

In the present description, the steps described in the program stored inthe storage medium may be performed either in time sequence inaccordance with the order described in the program or in a parallel orseparate fashion.

In the present description, the term “system” is used to represent anentire set of apparatuses or processing units.

As described above, the present invention provide the great advantagethat a spurious contour line is prevented from being created in an imageincluding a part with gradually varying pixel values and it becomespossible to perform high-efficient compression at low bit rates.Furthermore, it is possible to perform weighting on the color differencesignal even in the case in which the quantization parameter QP_(luma)applied to the luminance signal and the quantization parameterQP_(chroma) applied to the color chroma difference signal can havedifferent values, which can occur in the process according to the H.26Lstandard, and those values are represented by a single parameter QP incompressed image information.

The invention claimed is:
 1. An image decoding method for decoding a bitstream in an image decoding apparatus, the method comprising: receivingthe bit stream and a weight parameter that is added to a lumaquantization parameter; decoding, in a decoding unit in the imagedecoding apparatus, the bit stream and generating a chroma component ofquantized coefficients; performing, in a dequantization unit in theimage decoding apparatus, dequantization on the chroma component ofquantized coefficients using a chroma quantization parameter calculatedon the basis of a luma quantization parameter weighted by the weightparameter; and performing, in a transform unit in the image decodingapparatus, an inverse orthogonal transform.
 2. An image decodingapparatus for decoding a bit stream, the apparatus comprising: means forreceiving the bit stream and a weight parameter that is added to a lumaquantization parameter; means for decoding the bit stream and generatinga chroma component of quantized coefficients; means for performingdequantization on the chroma component of quantized coefficients using achroma quantization parameter calculated on the basis of a lumaquantization parameter weighted by the weight parameter; and means forperforming an inverse orthogonal transform.
 3. An image decodingapparatus for decoding a bit stream, the apparatus comprising: areceiving unit that receives the bit stream and a weight parameter thatis added to a luma quantization parameter; a decoding unit that decodesthe bit stream and generates a chroma component of quantizedcoefficients; a dequantization unit configured to perform dequantizationon the chroma component of quantized coefficients using a chromaquantization parameter calculated on the basis of a luma quantizationparameter weighted by the weight parameter; and a transform unit thatperforms an inverse orthogonal transform.